Ignored my gf due to feeling depressed, now she has new bf

Hi, everyone, this is my first time here, thank you for reading in advance. I have something that really bothered me all along but even more severe now and would really appreciate you guys' inputs. I know this could be a little long because this is the size of how much I am being depressed about so I hope you guys can really help me, thank you again.

The situation is this:
I had an argument with girlfriend over text back in middle of November of 2016 over something quite trivial but I have been having stress and depression problems that she may not know of. I never said anything about breakup or even hint it. I ignored her a few days, she sent a message asking do I want to talk to her talk face to face, all I said was "I dont know what to say, please give me some space, I want some time alone". She then want to confirm that if I meant want some time or wanting to break up with her. She then apologized and know it was her fault, but I didn't have the mood to reply. I have checked up on her social media from time to time during my alone time because I care about her, she did make some posts her thoughts about sad she was from time to time and she went out with her friends to have fun because I know she just want to occupy her pain. I feel bad she is sad too but I just didn't say anything to her. Then until this month, 6 months after our argument, I have learned she has gotten a new boyfriend, and I feel like sh**, because all I wanted is just be alone for a while, not a breakup.

Some background about my mental health is I have always been someone who could get sad easily or just all of a sudden, but it never bothered anyone so I never looked into this problem.

She is my first and only girlfriend, because I dont find girls just because I am lonely or for the hell of it. I love her and all but she did mentioned about wanting to get married and have kids before 30(she was 26 when we argued). This gives me stress more or less, but I never thought about backing out because I want to marry her, but I feel like there is a time constraint. Me being just graduated from college, working on my low pay entry level office job, on top of that, I couldn't even take care of myself yet, the idea of expensive ring, wedding, houses and kids is overwhelming. This gives me constant worries, what if I am powerless to fulfill those promises? what if I am wasting her time and youth?

Therefore, I work really hard, working 6 days, sometimes even 7 days a week with part time job on weekend waiting tables, try to save as much as I can to buy a house, or whatever expense I need for our future, as well as paying back college debt. Working so much also makes me feel exhausted.

English is not my girlfriend's first language, as a matter of fact, she is bad at it. So when she has problem with her school work that involves English, she pretty much depends on me with that. That means after work, or sometimes when my only day off when I only worked 6 days a week. I told her that she should put effort into learning English but she doesn't take it seriously. This also makes me feel exhausted and disappointed in myself because as her boyfriend, I want to see her grow and improve to be a better version of herself, and I failed.

I am the type of person that think I have responsibilities for all my girlfriend's problems and our future because as her boyfriend and as a man, it is what I should do to give her happiness, and this is just the way my mind works. But when I think I can't do it, I will have self blame, and thinking that I am useless, stress, and unhappy. This self-blame characteristic really took its toll on my mood and mental health on top of my tendency to suddenly feel sad. Besides the marriage stress, and the "if I can fulfill her goal" stress, I have other stress that I can't help to give myself.

For example, one time she has to go to New York City with a female friend of her to attend a nursing lesson. I have to work so can't go with her but I was really worried about her going to such a complicated place, even a female friend with her wont do much. That time I will have a feeling that I am useless and can't protect her.
Another scenario is when she goes to school in the city, my house is way closer to her school compare to her house (my place is around 15 to 20 min while her house takes an hour or more with traffic). She tried to look for an apartment in city near her school but its really expensive, but ultimately she found a place that isnt close but still in the city. She doesnt really like her roommates there though. When she comes to my house instead, I like in a small room so my bad is small, a twin size. So when we both sleep on it, it is not very comfortable. I told her to sleep by herself while I sleep outside the couch. She refused and want to sleep with me even it is not comfortable. This makes me feel useless and sad because I can't provide a place of comfort for her.

Because her parents are not living with her but over sea, she has siblings but some moved away while some come back very rarely. So she is pretty much living alone. She has to cook herself, but she, being an art student, her homework is time consuming. This is also why I always help her art history homeworks and online exams because the English stuff can take her hours. She is just so busy that she doesnt eat healthy and stress on her school work. She has become skinnier and skinnier, and this also blame myself that I can't ease her problem. I am also under the impression that I can't make her happy, I just can't help but feeling that way.

Because all of these stresses, which isn't her fault, makes me look unhappy in the relationship. She sometimes complain why I look unhappy. I just tell her that's the way my face look like. But in reality, I just sad that I feel so useless that I can't help her with anything, but I have been hiding my feeling because I know no woman want a useless guy. I feel it is a turn off for my girlfriend to show weakness and securities and saying how useless I am. I also didn't tell anyone because it just doesnt look good for me. Another thing is I don't want my girlfriend to think she is the problem and say things like if it is so stressful, then breakup. That is why all she see is me being unhappy, but she never know the why, and I am terrible at hiding my expression.

Before our break up, it was my brother's wedding, and I can see how stressed my brother is preparing it. Physically and financially. This inevitable project my ability to deliver the marriage to my girlfriend and this has been on my mind. On the day of our argument, I was working 6 days a week as usual, but I got a flu and really not in the mood. After I finished work from the restaurant, she want me to help her with her art history homework, I told her I am sick and can't do it. She wanted someone else to do it, I tell her she really need to do something about this English problem. We went into an argument, she said she isnt a good student and her talent is limited and I told her it isnt about is she school material, just want her to at least mediocre level, and all and all, I was really upset feeling that no matter how hard I try, nothing is getting better. Then I just lose it and say screw all this and ignored her, and makes me have no mood in the relationship but just want to take a break and be by myself. This is how it began. I had been ignoring her, but I still havent forgotten about her.

During my alone time, I was also got laid off from my job. The reason why I work so hard in this job is hoping I will get promoted from entry lever, so my salary raise, a step closer to our future. I even didn't take much optional vacation time because I want to show my employer that I am capable. The week before my layoff, I still got compliments from my manager and supervisors, it is like I am heading to the right direction to my goal. Then the next week, my position got selected to let go. That really hit me, my effort is all gone, feeling disappointed and I feel my goal of our future has become more distant. This really bring me down,with my mood being so unstable that make her unhappy again, I also feel I dont have anything to offer since I am unemployed. This made our silence even longer because I dont know what to say, not because I really want to ignore her. Knowing her has a new boyfriend further hit me.

I usually hide my feeling but I really feeling lost so bad that I can't help it but told my sister about it. She think I just feel jealous after knowing her having a new boyfriend, otherwise I would have contacted her before I know. This is not true, but I feel she would think this way, because it does look like it from outsider's perspective.

What do you guys think I can do now? Do you think she will think the same thing as my sister? Is it possible that I can get back to her if she know my perspective? I feel she really loved me but moved on, thinking I dont love her so I ignored her but that is not true. I really just dont know what to say and just wanted to be alone, that's all. I feel everything is too late now. Is what I did the wrong way to put my alone time in practice? I told her I want sometime alone, and in I just want to be alone, not like I want to be single. This really gives me a lot of regrets.