Who is the father? (Plz be nice!)

I'll try to make this short!

Last year I got out of a long relationship (8 years!) and started seeing my current boyfriend. Well, my new boyfriend and I got into a fight and I stupidly slept with my ex 1/20 but he didn't finish inside me. I had my period 1/23 but it was super light and short compared to normal. Got back with my boyfriend 1/25 and we slept together pretty consistently after that and didn't use a condom. I found out I was pregnant 4 weeks later. When I used a conception calculator it said my ovulation window was 2/1-2/6 so there's no way it could be my ex's baby, right?

Thanks...

Edit: Yes, my bf always cums inside me!

Ty for the responses 💗