Something important to consider in the relationship between Vin and Elend is how Vin felt about the way noblemen slept with skaa women. Were I Elend, after the scene in the first book where Vin asks him if he had ever bedded skaa women, I'd sure as crap wanna treat her with a lot more respect, no matter how attractive I found her. To me, the fact that you never saw Elend "checkin' her out" showed how strong their relationship was. The books also put a large emphasis on the trust in their relationship.
I thought the amount of sexuality in the book was just right. You were aware that Breeze and Allriane had been sleeping together (Brandon even confirms that in his annotations of WoA), and there is a scene that happens after the (newlywed) Vin and Elend have been having sex. It doesn't dwell on those things, just mentions them in passing.
Also, whoever pointed out that a lot of the others were tied up (I'm too lazy to look through this small thread and quote it), had a point. Ham was married, Kelsier had once been married, and perhaps wanted to leave it at that.
Spook, though. I think he's a realistically portrayed male. When he's younger, you've got the awkward teen with a crush on Vin. In HoA, there's that one girl in the one place that he obviously is attracted to. . . I don't remember her name and am too lazy to look it up. You know who I'm talkin about. It was made clear that Spook was very attracted to the girl in HoA, but you never heard him thinking "would you look at that booty, I'd like to . . . ". Even a teenage boy whose hormones are probably raging just as much as every other teenage boy's isn't automatically start thinkin sexual things about a girl he is attracted to. There's nothing unrealistic about the way men were depicted in Mistborn.