FMPAmelia - your post touched a nerve with me. As far as my FB was concerned, I cared about him and we were close as friends but it was never ever going to be a relationship. I know he wanted that and I couldn't give him what he wanted or needed. I do feel guilty that I hurt him. I never led him on though or made him think it would be anything morenthan sex.
I am sure you didn't lie- but my opinion is that in relationships people can be honest but still have spoken, or unspoken hopes.
Sometimes people equate longevity of a relationship with commitment or potential commitment.
I think the whole FB thing is a minefield- I have never known it to work successfully, but if it does- fine.
You see, people often think they know what they want, but that can change. I have heardloads of men say they slpet with women as FBs but the women became emotionally involved.
There are lots of features on this on the web and in publications- which show that biologically once a woman has had sex with a man, something goes "ding" in her head and creates an attachment.
Now you are living proof that it didn't - but as with all research, it's the exceptions that prove the rule.
As for not being a FB with a man because he asks , and doesn't want you as a date- isn't that double standards? if both people are happy to be FB, it really shouldn't matter who asks first.