YANBU that your personal experience causes you to question whether a new male friend might have a sexual interest in you. YABU if you think that the old adage that men can't really be friends with women applies universally. And IMO the posters insisting that NO ONE has ever had a real platonic male-female relationship (and posters who say they have/do are naive/deluded) are indulging in the sort of high-handed obnoxiousness that in another context would be criticised as "mansplaining".
I DO think that a lot of people, male and female, LOVE the idea of falling in love with/becoming a couple with an old friend. Look at Monica and Chandler, Forrest and Jenny, Jenna and Matt, Ron and Hermione, Dan and Vanessa ... you get along great, feel comfortable, trust each other, know each other's friends and family (and that s/he's not an undercover serial killer), have seen each other at your best and worse, know each other's quirks and history, have common interests and values ... just add sexual attraction and stir, right? This desire even manifests in same-sex friendships where neither person is same-sex attracted ("why can't I be a lesbian?!" "If only you were a man!") It rarely works, but it's tempting for a lot of people (although there's also the opposite pole: for example, the poster above who said that kissing her friend was like kissing her brother). But if people want to try it, I don't think that means that either or both people entered into the friendship fraudulently, just waiting for the sex. Or even that they had sexual or romantic feelings from the beginning.
And of course, loads of people don't even want to try.
I love all the women saying "well I have a male friend who hasn't crossed the line".... There's huge a difference between haven't crossed the line because the right opportunity never presented itself/unavailable vibes" and not interested So if someone here says she's confessed her undying love to a hetero/bi male friend and he's said sorry, I love you as a friend but that's all ... he's just playing the long game, biding his time to make his move? Or she must be a hideosuly awful physically unattractive beast? It's a self-fulfilling prophecy. There's always some excuse to deny something you're determined not to believe even when it's happened all around you and people who have experienced it first-hand are telling you so.