Conflicted

My fiancé- the father of my child who has cheated on me too many times to count in every way possible (from every dating site to whatever else "I have no proof of") wants to get married. I want so badly to believe that this time is different- as we all have at one point or another- but I can't. And his best friend- who just confessed his love for me- is telling me it isn't. The best friend wouldn't lie to me. I honestly believe he loves my son more than his father does. But I don't know how to handle this. I want to be responsible and independent enough to not need the father, but I don't want to make a hurtful decision with his best friend who just moved in with us. I'm so close to making a bad decision after everything he has put me through, but I don't want to be like him. But.. The best friend genuinely loving me AND my son more than my fiancé does makes it so hard... I'm so confused. I know the three answers. I know that all of them are wrong and I know that this situation in general is HORRIBLE. I'm so ashamed. I've never been in a situation like this. But I don't know what to do. Please help me.