Should I forgive my girlfriend she lied to me a lot

As with the other thread(s), this is just more of the same. You forgiving her for being dishonest is not the big issue in your relationship. There are red flags everywhere.

At this point in your life it sounds like you don't yet have the skills to be in a successful relationship. You need to just exit the relationship and focus on yourself. Maybe a few months down the road when you have gained some self confidence and emotional maturity, you will be able to better approach a relationship.

Forgiveness is healthy and liberating, I always advise it.

Lies will be followed by more lies and soon she will be controlling you. I would not forgive at all because there will be no end to it. Turn tail and run.

I think you need to step back and ask yourself where you see yourself in this relationship. And when I say "where", I mean in terms of who it is you are. Don't let this person define who you are. You be yourself. Please see your value outside of her presence and understand she is her own person as you should be as well.

Clearly this person does not know how to communicate well. Just for the record, I don't know if she is lying or just so unorganized that she can't facilitate plans well and get her ducks in a row. My daughter use to be exactly like this. She could never make up her mind what she wanted to do, so she would prioritize then un-prioritize. If I could use my daughter as the example here, I think it's safe to say this girl you know is at bare minimum not prioritizing YOU.

So whatever the reasons are, you keep getting kicked to the back. That's what I see based on your overview. If she's actually giving reasons and you know they are false, then that's much worse. I've never been much on " I love you" when it's servicing a stab in the back. But before you reach that conclusion, just ask her why she had to keep changing times. If you feel it rings hollow then you need to decide if this is a person you really want in your life.

People make time for people they care about. Yes, sometimes schedules get crazy and they are not helped if the person in charge is not well organized. But you need to get to the root of what actually happened here (beyond assumption). Is she lying or just a lousy organizer of her time? Trust me. She wouldn't be the first one to be a bad organizer. So ask her and see what she tells you. This might need to be a two-part question. Let us know what she says.