Scared, alone pregnant

So I told my bf I was possibly pregnant we had sex once when I was ovulating even though I was trying to avoid it.. I’m supposed to start my period Friday and I’m having none of my normal symptoms. He keeps saying it’s not possible there is no way I could get pregnant. Unless he got a vasectomy without my knowledge there is 100% a very good chance I’m pregnant. We had our son in December and we have been fighting like crazy for the last week to the point we may break up. I’m really scared about being pregnant I’m scared to tell him if I get a positive test... I always wanted to do something cute but I don’t even want to think about it bc he’s going to be mad

Update after some comments:

I was on birth control it came out. Yes he was aware it fell out.

Also don’t be rude.