Welcome to the site. There are some pretty neat people on here, but also plenty of obnoxious and/or frustrating ones. Funny stuff and things you'll find odd. Hopefully this does work out as a good compromise with you and your sweetie. I would personally be cautious, if you already know he has cheated on someone once. That being said, have fun.
The Etc section is amusing to poke around, Women's Issues has a lot of shit posting and a fair few ladies (myself included) are getting a bit.. territorial in a way about it, given how often a handful of individuals like to mansplain or try to make everything about their dick. The Ask a -blank- sections you can ask people of that demographic questions, seek opinions, etc. If it isn't a thread you yourself created, unless it is in Ask a Woman ya aren't supposed to respond (hopefully to prevent any confusion for you).
If you want to ogle there are multitudes of men who would be happy to show off for you. If you're interested in things besides the almighty peen there are plenty of sections on the forum for those too
As far as understanding, my sweetie and I don't one on one chat with anyone on any forms of anything in a remotely pervy way. We both have accounts on here (it's actually how we first got introduced and started talking), he knows I'm flirty but loyal as hell. Neither of us show ourselves off really, not since we've been a couple. I know some folks do need their ego fed a lot, but just for myself I wouldn't be too comfy with that. Whatever works for you both, though.
Cheers,