I hate my boyfriend's mother.

I need advice. I have been absolutely appalled by the way she has treated her son in the past. And how she has treated mine and her sons relationship. She is supposedly a Christian woman. When she found out her son and I were having pre-marital sex she lost it, asking him "What are your convictions?!?" And having a meeting involving my parents as I was under 18. She demanded we agree not to have sex again until we are married. She has "tried to accept me, and treat me like family" (direct quote) but as I ruined her and her sons relationship by tempting him with my lady parts. But as a "Christian" she wouldn't have had 2 affairs and be living in sin, right? Have any of you ladies had issues like this? Can you help sister out?