Certainsomething,
I completely hear you about today's society and its preoccupation with being thin. I just want to warn you, as you probably already know, girls are extremely sensitive about their weight and will pretty much catch on to any sort of mention to it, even if it's meant to be harmless. My best advice on trying to get your girlfriend to a more healthy weight is to suggest something you guys can do together that you'd both enjoy that doesn't sound like exercise. Take her out on walks every day or bike ride together. Just be gentle and dont force her. This might also bring you two closer together, though from the sounds of it, you guys sound pretty close already!

I can also understand your roaming eye. It happens to the best of us. I dont really have much advice other than what has been given except that sometimes when I'm with the guy I'm dating I gauge my feelings for him by looking at him, and if I feel proud of him, proud to be with him, and proud to show to the world that he's with me, either by holding hands or something along those lines, then I know that at the moment i wouldn't want to be anywhere else, and that right then he is the one for me. And if that's true for that one moment, then I'm willing to keep working towards always being with him until that's not the case anymore. I'm not sure if that really makes as much sense as I want it to, but I'm not sure how else to explain it.

I hope this helped at least a little!
Take care
Ro