My last period was may 8th, my cycle is usually 27days. I done a thing online to see when I concieved and it was either the 21st or 22nd
What Alaysha said. Even though a condom is 97% effective it's still not 100% and it only takes one escapee to get you pregnant.
The only way you'll know for certain is with a paternity test once the baby is born.
I guess it depends on when you guys had sex and when you ovulated and all of that, but it seems much less likely, to me, that the other guy would be the father. I'm sure I would be paranoid also though.