Feeling uncomfortable about bf's dirty past Watch
B. Yes, birth isn't a particularly 'pretty' thing, but that's his child, he helped to create it, there's nothing weird in watching it being born. It's not a dirty thing, it's natural and some may say beautiful. I'd possibly say you're just nervous or scared about it for when you eventually (may) decide to have children.
C. His past is his past. You can't change it. But remember he has moved on, he is with you. He has been with you for a considerable amount of time, that surely counts for something?