Ex boyfriend

Hi guys, I was with my boyfriend for a year and half and two months ago we broke up and I was heartbroken because I loved him to pieces and he took my virginity. However two weeks ago I was at a party and I was drunk and I slept with one of his friends and he's been wanting to speak to me since. What do I do? Should I feel bad? Because I know my ex boyfriend knows and apparently he's heartbroken but he still doesn't want to be with me😔 someone suggest a idea please