I just want to cry I am a side hoe

So this guy I hooked up once with hit me up again and told me he wants to do it again Bc it was so good but he has a gf so obviously I said no and he's like well we had a fight and whatever so since he said they broke up I ended up agreeing to him coming over my house and things happened and after we were just talking it slipped out that they are still together and just had a fight and I froze because while he was sleeping with me his girlfriend was probably home thinking he is asleep and Ik it's not my fault but I never felt so shitty in my life and I can't stop thinking about it 😭 like he didn't even feel bad about it like if it was okay to cheat on her with me .

Update he deleted me from social media so I can't stalk him to find her