I'm in a relationship currently but my ex is starting to come back into my life.
Why are you allowing your ex to come back into your life?
Because I can't choose to live without sex and his attraction is just way too strong! So I'm going to cheat on him.
I understand having a strong attraction to someone, but you shouldn't be leading this person on if you don't feel like being with them. I highly recommend breaking things off instead of outright cheating on them.
I don't think your opinion matters, who cares if he gets hurt?
Try to put yourself in his shoes, realized all the hurt that you would put them through. Breaking up with them will still be hurtful, but it would be a lot less harmful than you cheating on them.