Most likely it is the boyfriend but it could be either.
You had sex with "a guy" on day 7 of your cycle. You had sex with your boyfriend on days 14+.
Sperm can survive about 5 days. You'd normally ovulate between days 11 and 16 of your cycle (Dec 5-10). If you ovulate early and there was a failure of the condom or it wasn't used properly then there is a chance.
A DNA test can confirm. Again, most likely the boyfriend is the father