angies: It sounds to me like every one of those examples was pursuing you as a love-interest. (That's not BAD, per se, it just would be nice if they made their intentions clear up front, ya know??) Most attractive girls have a number of guys who "hover" around, pretending to be friends, waiting for their Big Chance. (Girls do this too, btw...) This is classic Nice Guy Syndrome, which I prefer to call Disingenuous Insecure Bastard Syndrome. Having been there, done that, I think it takes a pretty secure guy to honestly just be friends with a very attractive girl, esp. if he doesn't have a solid alternate love-interest.
Another thing is... You know how a lot of men don't know how to relate to women as people (as opposed to sex-pursuits)? A lot of women don't know how to relate to men without getting their flirt on. Like it's a natural instinct: "Oh, hey look, there's a guy, I'm going to make him attracted to me to help validate my worth as a woman! Even though I have a boyfriend, husband, whatever..." (I have no idea whether you do this or not, of course, but I am myself guilty of sometimes "practicing" on women I have no actual sexual interest in. Sometimes you *catch* the car you're chasing, and you go "uh ohhhhh"...
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I sympathize; it really does suck. I like women as friends, I really do, but it's difficult. Friendly gestures are interpreted with sexual overtones, boyfriends get jealous, etc. And we really are programmed to value sex with a pretty girl so highly. Makes us act like jerks!
I do think it's a shame to write off ALL men as friends, but I've been here with girls at times. Best I can say is... try to befriend guys who already have girls/wives they love and if they get more than friendly, be prepared to break it off and never look back.