I believe what you have described happens a lot, and it did happen to me a couple of times, but them this is not a genuine friendship. It's one thing to start as friends and an interest grows, and another thing because of interest you want to be friends. People need to be upfront and honest. And that could also lead to friendzoning which is not ideal. Also, sex is different from wanting a relationship. Sex is very personal and for some people has nothing to do with feelings. THank you for commenting :D