Cheating is never okay right? EVER

been in love with a good friend for a year In a half. he got a girlfriend. when they were on a break we hooked up randomly. didn't want to continue it, but it keeps happening at least for the last few months. I think he is back with his GF now but tells me and my best friend he is with her for the wrong reasons and doesn't love her. I don't know what to do. I'm being so so stupid..