Always, always, always believe a guy when he says he can’t give you what you want.
Unfortunately for you, you accepted the FWB from the get-go and that is probably the only thing you will ever get from him. He sounds like a nice enough guy, but he is getting exactly what he wants (sex, friendship, the appearance of a relationship with absolutely no obligation to you whatsoever, because you agreed to this FWB situation) therefore, he has no reason to do anything different.
Right now you have a few options. You can sit down with him and have a serious (but with no accusations or demands) conversation with him and say something like, “Simon, I really like you and I have been enjoying spending time with you, and I mean everything that goes along with that, but for me, I really need to have something more, not just a friends with benefits kind of situation. If we stay together, I really need to have a real boyfriend. You said you don’t want that, right now, but can you see us together as a real couple in the near future?”
If he says no, then you should politely bow out of the relationship right now (unless you have changed your mind and you don’t mind being just his FWB chick).
If he says that he might be able to see you as his girlfriend, but just not right now, then you should tell him that for now, you guys have to cool it (that means no sex, no sexual situations, not hand holding, no cuddling, no making out, no kissing, no sexy or lovey-dovey talk etc.) but if you want to still be friends, cooling things down could eventually lead to him changing his mind and wanting you as a girlfriend. But be aware, that if you slip up just a little bit, you’ll be right back to FWB and you will never give him any incentive to want anything more.
He also might say no, and he also doesn’t want to be just friends. In that case, you are done.
If you guys do cool it (and remain friends) or break up altogether, and he comes back later saying that he wants to get back together with you, tell him that you won’t even consider it unless he is willing to try out a real girlfriend/boyfriend relationship, otherwise FWB is all you will ever get from him. Good luck : )