Your mother deserves a life doesnt she?? Should she be mean to anyone YOU bring home?? Just because things didnt work out between your mom and your dad doesnt mean that either one of them should give up on life. If the guy is nice to you.... you be nice. If he is a jerk..... then you be a jerk
what are you usually like? I say be indifferent that means don't be either mean or nice. this is how you can protect yourself from being hurt emotionally. give it a time limit before you act any way like 12 months or something.
My mom had many boyfriends when I was a kid & it seemed like the ones I liked were the ones she didn't like. It sucks that your mom isn't more selective about who she brings home. Just the same, be cordial, not rude. After awhile I just started to keep my distance so as not to get too attached to someone that I would likely not see again.
Cut the guy some slack - talk to him on your own - make up your own mind if he's a guy you can connect with. But, in the meantime - have a private talk with your mom - don't pout or get aggressive - tell her that her string of boyfriends is bothering you - maybe she appears desperate - maybe she is not giving you the attention you deserve (here's one of those universal rules: you, the child, get first dibs on all parental attention - until you're a lot older and independent). The guy or guys are not the problem - your mom's behavior is - here is yet another case where the teen has to parent the parent.