Im shocked and don't know what to do

i made a huge mistake... So i been with my boyfriend for 2 years and a half now... i go to college.. Well i hung out with this guy because i known him since high school. So we went to his house to drink with friends, i had sex with him while drunk😫 this was 2 months ago... I cheated on my boyfriend the worst part is that i FOUND OUT im pregnant!!!!!! And i think it's the other guys baby. because me and my boyfriend been having sex for a year unprotected and i haven't fallen pregnant but now i'm pregnant and i can honestly say i think it's not his.. i feel grosss and a mess! i don't know how to tell my boyfriend... Should i abort it? I didn't know i could be pregnant that fast with someone else rather than my boyfriend ! Should i take a pill and do it?