The underlining thing here is your comment about friends with benefits. I've posted this before a lot about situations like this, so here goes my take.
ONCE you sleep with a guy without establishing an emotional connection, meaning you are foregoing the relationship in favor of sex, than his opinion of you CHANGES IMMEDIATELY. He may like you, think your cool and attractive but you're a sex toy, a willing sex toy as that. He may have wanted a relationship but as soon as a guy is confronted with "no strings attached",especially before you tell him you like him, he will take it and that IS THE ESTABLISHED RELATIONSHIP.
A few other things, we as guys, take certain things into account with F-friends. We will consider whether you have done this in the past (not attractive), why date a girl when you can have the one thing hardest to get with no effort at all, and some others.
A relationship allows you to grow on what you already know of the person, so like I said, he may have thought you were hot and liked you but once you gave it up to him the situation KILLED the possibility of growth and getting to know you properly.
I know it sounds harsh, but a F-friend into a boyfriend is one of those things that RARELY happen, I haven ever even considered it and have never heard it happen either. Your fighting a very hopeless battle. All I can say is in the future think twice before you give yourself away for whatever reason, its not that all guys are pigs but if you play along than it is you that walked willingly into the lion's den. Your better than that