Help !

Ok so Im in quite a tough situation. I'm 20 weeks 4 days pregnant the first day of my last period was august 7th and lasted til the 11th. my cycle is about 31-32 days. I had a one night stand when me and my boyfriend broke up, that happened on the 21st at around 4 or 5 am. I can't remember if he finished or not if it matters at all I believe he had been drinking a little and possibly had smoked pot before we had sex. Me and my boyfriend made up and had sex on the 25th at around 2 am which on my period tracker said that the 25th was my ovulation day.I then had sex with my boyfriend on the 29th and the 31st. I found out I want pregnant on September 6th at around 9pm who has more of a chance of being the father? The anxiety of not knowing is killing me . I love my boyfriend and really hope that he is the father