Of course Kermit loves Miss Piggy. Look at his face when she starts flirting with other guys. Look at when he first sees her in TMM. For that matter, look at his reaction when she walks out on him in TMM. The other movies are more of them performing than expressing their actual emotions, at least in my opinion, but still. It is very clear to me that he loves her.
Of course he gets sick of her occasionally and flirts with other girls when she isn't looking. But you can't really blame him, I mean, look at how controlling she is. She won't let him so much as say another girl is talented, and yet she throws herself at every good looking guy she comes across.
So, does Miss Piggy love Kermit? That's debatable. She is awfully obsessed with him. But, like I said, she throws herself at every good looking guy she comes across. On the other hand, she always comes back to her frog. So basically, in my humble opinion, she loves him, and has a crush on all attractive males.