Hi so i had sex with my partner for most of my fertility window and had sex with another guy the day i ovulated but he didnt nut in me at all but now im 8 weeks pregnant , i want to make sure my bf is the father?

The erect penis is secreting sperm containing semen continuously. It only takes one. In the cited scenario, there is only speculation on who the dad could be. A NIPPS test test done on maternal blood as early as 8 weeks can find cell free fetal DNA that can be used to define paternity. This test holds up in court. It is best never to be surprised at delivery & often obvious when you guess wrong.