How do I know if he's cheating..?

From the beginning we were a little bumpy. But then after about a month and a h,af everything was great. We've been together for about three months now and as far as I was concerned everything was good. But then he started to seem a little distant, he would still talk but he wouldn't seem like himself. He has a ton of pet names for me and he usually calls me them all the time and he hadn't called me any of them in about two days before inbrout it up. I had asked him what was wrong a few times and he kept telling me it was stress. To be fair, he probably really is stressed. He's going trough some things. But from the beginning there was this girl, she met him when he was living in Florida, he no longer lives there. He lives like 10 states away. Well, she would occasionally post things in his wall and I hate them, he knows it but I didn't give it a second thought because he never commented anything on them. I know it sounds a little creepish, but I would go to bher profile occasionally. It was always private, until last night. Being a girl who was already insecure about the relationship for the last few days and being insecure about herself I looked at her wall. Turns out he had been posting things on her wall like, 'super like the new pic.' or 'like the new pic' they would have comments on them and she would ALWAYS put a heart or two or ten in her comments, but he only put one heart in one of his comments on each post. As I got into later posts, like early April, he had one that said, 'well played love :P' he calls me love all the time. I guess being called love could go either way, friends or more. I think there was one mid may that said 'cutie you're the best' then there's one in the very beginning of our relation saying something like, 'hey, I jsust wanted you to know that your new pic is amazingly beautiful and I love you.' I don't know what to make of all this, I mean..she's in Florida so he can't be physically cheating, and his personality is flirty but I still don't know what to make of all this. Should i be concerned? Or should I just ignore it and try my best to not go on her profile. And I understand that it's Facebook and not to believe everything I see on there, but he wrote it so it's a little different..anyways, should I be concerned?