Hi again! I couldn't finish my first post below because it was too long, doh! So read the bottom one first and then read this lol.
Couple years later, I am now on speaking terms with my mom and I now live with her and her husband (the guy she started dating after she left my dad). And things turned out ok. I never spoke to him until I moved here last year lol. So I was pretty much forced to deal with it. It helped me grow as a person I guess.
I know how hard is must be for your mom to start dating again. And I think you have every right to be upset that she basically forced you to interact with him so soon. You can let her be happy with him, but she shouldn't make you do something you're not yet ready to do. I guess the only thing you can try to do is talk to her about this.
I hope everything works out