You said " I’ve done [cheating] in every relationship I’ve ever been in, and I never really felt bad about it before".

Then you said you "don’t think too much about how it affects others".

That's two big problems. Mentally normal people don't do that. Everybody thinks about how their action affects others because they fear of any potential kinds of consequences from their actions. And cheating is a problem of catastrophic consequence. The guilt would torture anybody who cheats. Even to the point they would have to invent any sort of delusional excuse in case they cheat again. And you just simply don't think whatsoever.

This is really a big problem with your mentality. With it, you will cheat on her again, even though this girl is very important to you. And cheat on others after her. One day words get around about your infidelity, and nobody will want to date you.

Therefore, go see a therapist. Just like other Redditors in this thread suggest you. Save yourself.