Sex and Christianity?

I'm 17 and I've been with my boyfriend for a year and 3 months. We are a well suited couple and have never had a proper argument or anything. Anyway, we've done pretty much everything except sex. I don't know what to do because I really want to have it, but I'm stuck. My mum is a serious Christian and thinks I'm innocent obviously wants me to wait till marriage to lose my virginity. However, I'm not so strict on this rule (I'm Christian too). Also I can't talk to her about contraception because of the situation. I want an implant. I have three older, adult  brothers and I spoke to two of them who are atheists and they said I should have it if I'm safe and both my boyfriend and I are doing it for the same reason. I thought they'd be very overprotective but they were so supportive instead (to my relief). 
I want to wait till I'm 18 anyway but what then?! (My boyfriend is respectful and doesn't mind waiting - is just the whole mum situation) I fear what she'll say and if she could stop me seeing my boyfriend. 
Help please :S