Help!!!

So I'm 17 weeks 2 days. I'm confused with who the daddy. I had a d&c dec 13. Never had a period. I found out I was pregnant Feb 3 and hcg was at 50. Well me and my boyfriend split up and I went back to my ex husband and slept with him from the 6 to the 12th of jan. And then we decided we didn't want to make things work so went back to my ex bf cause we said we were going to make things work and started sleeping with him from the 13th of jan and on. Well my due date is oct 14 2017. So who's most likely the dad?? They both know too. BTW it's a baby boy!