What’s going on here.... Help me:(((

Okay so, I am in a relationship and it’s amazing he’s super sweet. I have never been in a relationship with a guy like him before, he treats me so well. Yet, I don’t think I like having sex with him, I don’t get horny anymore. My ex thing has been texting me recently... I’m so very tempted to meet up with him and hook up with him BUT i know that would be wrong of me because I don’t want to hurt my boyfriend. He’s the sweetest and it would break my heart if I hurt him. What do you think is going on with me???