Which do you think?

I was in an open relationship I always let my bf ejaculate inside me and the other man always had to wear a condom. Now I am pregnant 
I got my first positive opk on jan 29. 
Me and my bf had sex jan 26,28,29,30,1
Me and the other man only had sex once jan 27
He used a spermicide condom and pulled out!
I am worried because I don't want it to be the other mans baby
Due oct 24
Please nothing negative as they both know about each other just whos do you think it is?