Lost my virginity, now i’m regretting it.

( i’m 18) hi everyone... i lost my virginity on valentine’s day with a guy i was dating for a month. he was bestfriends with my bestfriends boyfriend, and i felt i could trust him so it felt right and it wasn’t forced. but now i’m regretting it. I got back together with my boyfriend that I had been with for 4 years and i’m completely in love. More in love than before but we always talked about waiting until marriage and I broke that... i feel awful and don’t know how to tell him. I know he would probably still want to be with me but ugh idk.