Father's Infidelity and my depression

Hi everyone my name is Laura and it took a lot to muster up the courage and post this. Please be kind in your comments. This is very new to me and I'm at a loss at what to do.

I found out fairly recently that my father cheated on my mother multiple times. I knew there was an instance of cheating before I was born but I didn't think about it and grew up in a mainly loving house, believing my mother and father loved each other. My dad's anniversary cards were sweet and sentimental. A few years ago I used my dad's phone to check the internet and I got a notification that my dad got an email - from a woman. I checked his sent inbox and found there were emails to a lot of women, one even saying he wished things had been different and he hadn't married my mother. Needless to say, I was horrified. My mom had no idea. There was some screaming and fighting and a few peaceful years passed - or so I thought. A few years later, we found out through my dad's emails that he was at it again, and this time, my mother didn't forgive. Me and my mom kept reminding him of his evil actions, which eventually for a few weeks, he became suicidal and landed himself in the psych ward. The psychiatrist just determined he needed sleeping pills and they sent him home. From then on, my mother and I resolved it was best not say anything, for her not to express her hurt and betrayal and me, not to express my anger at him, otherwise he will land himself in the psych ward again. Both my mom and dad are middle aged, and my mom hasn't worked since the 1980's. My dad is the only source of support for all three of us since I don't have a job right now. There is occasional screaming and cursing, with my dad threatening to become suicidal if she brings up what he's done. My mom is a hard working and selfless woman who has always had her family in mind.

Now, I'm in a long distance relationship with a very wonderful man and he has not shown signs of infidelity, but because of this situation, I don't trust him and I find myself fighting with him almost every time we talk. All my life, I had a specific image of who my dad was and looked up to him. Now, I feel he's a stranger and a ghost of someone I don't know. I'm 27 years old and this is the first time i ever knew my dad was like this. This has put me in a great depression, made me sad and angry all the time, and I have moments when I want to break up with my boyfriend and just be a single person, just spending the rest of my life healing from this. What should I do?