Let me get this straight.
You met a guy off a dating website; websites which exist to make males and females hook up. Males don't talk to other males on these things unless they're gay - it isn't for friends, it's for flirting, hookups and relationships. You add this guy on msn and have conversations.
At some point you get a boyfriend, his girlfriend becomes his wife. You still talk to him. To be honest, for me this verges on some kind of emotional cheating since it's placed in a dating context - you found him emotionally/physically attractive otherwise you wouldn't be talking to him - and he would feel this same way.
He's clearly a sleezebag - he's married and on a dating website talking to a girl 15 odd years his junior. You continue to talk to the guy, even though you have a boyfriend - and he start propositioning hotels to meet up and have sex - you still continue talking to the guy. And now you're detailing the situation to us - you clearly know what he's asking, and the only thing which you say is holding you back is your boyfriend, his wife and your age.
Let me say this: you have and are emotionally cheating on your boyfriend with this guy. The fact you haven't deleted this guy even when propositioning sex to you is evidence of this. If you want to be with your boyfriend; delete this guy, tell your boyfriend about him and apologise for being so naive - which I'm not at all convinced you are. If you meet up with guy, I have no words to describe your character.