I think I might end up cheating on my relationship even though my partner is really devoted
Why would you cheat in a relationship when you have a partner so devoted to you?
I am not in love with the person
If you are not in love, then it is best to break off your relationship. You are not being honest with your partner by staying in the relationship because he thinks that you are as devoted to him as he is to you.
Eh I could still just have sex with other people.
That's not a good way to think about it. He sounds like a great guy who deserves someone as committed as he is.