What on Earth am I supposed to do?

Im 19, just out of college. Im engaged,we've been dating for a year and a half. we've set a date three times and have postponed it all three times due to his family disagreeing or lack of funds.He is an amazing guy. So patient, understanding, a gentleman. He's a nice guy, it almost stops at that. I feel like the fire that was there once isn't anymore. I think it's my fault. He puts his every effort into it, and i am just numb really. When I think about us walking away as friends my heart breaks, and i cry. I dont want to lose him...And when his ex girlfriend was talking to him I was so mad and jealous that she was talking to him. The worse part is that I can't focus on our relationship 100% because im side tracked by another guy... I feel so awful like a hypocrite. How dare i throw a fit of him just talking to a girl, and im falling for another man (we have never been physical). This other man happens to be married, so thats just the icing on the cake. =( Despite everything the guy on the side says about leaving his wife if things between us get serious, i just have a gut feeling that's a line of crap. Realistically, he wont divorce her, even if he did, he'd probably cheat on me too. Not to mention I know that as soon as the "newness" of that relationship is gone i will probably regret making that decision. Ive told my fianc�e not too long ago that i couldn't drown in this relationship anymore and it was a cry fest and he was so hurt, the look on his face killed me along with the statement "I loved you, I would have done anything for you"...But im still sitting here with my selfish wants. Im lost on what to do... Rekindle a dull love with a guy who has no clue what he wants in life because of our foundation and amazing friendship and life we have shared so far? or respect him enough to let him have his own happiness? Or be the home-wrecking mistress to this man Ive only been in touch with for two months?