Need Advise

I have been pregnant for 29weeks and a few days, I had sex with my ex some days after my mens 6th or 7th Feb ( if not mistaken) on the 23rd Jan and with my new boyfriend on the 13th of feb but prior to that, I had sex with my current bf on the first day of my mens and now I can't figure out who the father is and keep wishing it's my current bf's cos I can't stand my ex ...after checking n double cross checking online using these calculators that determine when you conceived, it keeps pointing at my ex and am devastated, feel like i dont want the baby anymore please any advise?