Am I a horrible person?😢😢😢

I've recently gotten close with one of my coworkers we talk a lot more than we used to and are able to confide in each other, give advice, etc. I don't see him as anyone I would really date because he's a huge flirt who sleeps around and doesn't commit to any girl because he doesn't see the point in settling down with a girl while he's still young (22). That's fine if that's what he's into. Anyways. The other day I dropped off something for him at his house and I truly had the intention of staying for a minute and then leaving then we got talking and laughing and before I knew it we were making out like crazy. He initiated all of it and yes I did go through with it because what harm could it bring I thought we're just friends. Then I gave him a blow job. It was the heat of the moment like there was no romantic feeling although I did feel a bit ahead of myself. Then I find out like 3 days later that he is 'wifed up' as he put it and has been with this girl for 2 months. I felt terrible because if I had known that he was seeing someone I would have never even kissed him let along given him a blow job. I confronted him and was like why didn't you tell me. Like I don't need to know your business but it's a good idea to let someone know you're in a relationship. He just shrugged and said what's the big deal you're the one who sucked my dick then he walked away. Am I horrible???? 😢 I really had no idea that there was someone else. I feel awful! What do I do?!?!