Hi 123Bunnygirl456,
welcome to beyond blue.
The reasons why a partner might cheat on the other person are many and varied. There is nothing wrong with you. I maybe a little old fashioned with what I about to say, but if two people commit to each other, then ..... I think you know where this is heading.
Putting aside the your current partner being on a dating site, have you consider other possibilities why he might not initiate sex? I can only speculate, so this might be something you might consider talking to him about.
What do you want to do?
Tim