Is my life over? Huge mistake...

I have a 8 month old with a fiancé who I love more than anything. We broke up and I was tired of his shit. He was my one and only and we broke up for only a week. September 5th I had sex with someone else let's call him john. It was a huge mistake.. it wasnt good at all and I immediately regretted it. There was nothing I could do the damage was done. He didnt use a condom he pulled out. Well me and my fiancé had sex that night after he called me begging me back crying saying he would change.. (ugh gross I know but it happened) he didn't pull out actually. And we had sex again on the 7th and the rest of the month as we were back together. He never pulled out. Then I found out I'm pregnant and I cry every night. I feel depressed because there is a slight chance it is johns right? If I tell my fiancé he will never talk to me again and will be crushed. Idk what to do. Honestly someone help me.. yes anonymous because I am ashamed.. I did a horrible thing ugh i don't wanna lose him I'm 14 or 15 weeks pregnant as of 12/1/17 the doctors haven't chosen a date because I didn't know my lmp date.. help what would y'all do please, *update* real quick thanks some for commenting and helping me, I have had a ultrasound and since some babies grow at different rates at this stage they didn't know rather to go with 14 or 15 weeks, they are leaning more towards 14 weeks, which means I wouldn't have ovulated on the 5th if I ovulate on the exact 14 day mark but idk if I do because my periods weren't regular, I can't find anywhere in Florida that does a in utero DNA test.. or I would get that done secretly. I will not get a abortion ive seen the baby and TBH it looks like my fiance already to me.. god help me 😭Ive been with him since I was 13. I dont wanna lose my family. If I tell him he will never talk to me again and then it'll most likely be his baby and itll all be for nothing. But if idon't tell him the delivery will be so scary for me trying to figure out who the baby looks like and ill cry to myself feeling awful. Am I evil to not say anything? It took me three years to conceive my first so I thought there was no chance at conception which is why my fiancé always cums in me just incase it would take another 3 years we wanted babies close together, we thought it would take a long time..