in response to Jed:
I think that Dean is very self-conscious and is unsure of himself. As a result i think he wants to make sure he is pleasing Marylou, and the only way to truly find out is to see how she would react with another man. By Sal not having sex w/ her in the end, I think it proves that he is being a good fried, not that he views women differently than Dean. Whether it's because Sal doesnt want to compare himself to Dean, or just because he feels awkward betraying his best friend, i think that Sal doesnt make love w/ her because he doesnt want to hurt Dean. I agree w/ Jed that it is very weird and creepy, but it just goes to prove how much Dean is willing to sacrifice in order to gain some sort of identity and feel more comfortable about himself.