Am I just a 'bit on the side' in another country?!

So in January I met this guy online and we started talking on Skype. We talked and cammed all the time. I stopped going on Skype and then he asked for my number and we started talking and sending pics on What's app from there. We've talked almost everyday since February.

Im 21 from England and he's 29 from Australia. When he came to England on holiday a few months ago, we slept together. I thought that was it. But even after he went back to Australia, he still messages me everyday. We mostly talk about sexual stuff and gym etc and not much about each other's lives. He visits England on almost a yearly basis.

He never mentioned adding me on Facebook, and I found out why- he's had a boyfriend for over 3 years- i saw this by finding his profile and adding it with a friends account. He doesn't know that I've found out. Obviously he's a cheater and stuff, but does he actually like me? We are on the other side of the world so its not like he's forced to see me, but he still messages me on a daily basis when he wakes up and throughout the day or before he goes to bed. He says that he'd like to visit again and stuff. He tells me my that body is top quality and that what we made that night was pure passionate art.

If he was just looking for sex, why is he saying these things to me? Why is he still talking to me on a daily basis even though I'm not even in the same country? Even though he has a boyfriend!

Does he like me or am I just another 'bit on the side'? Should I tell him I know? If so, how?
Or should I play along with things and try and find out some more stuff?
What should I do?!