Opinions on FWB with best friend?

I'm going to try to explain my situation as best as I can. So earlier last year, I became friends with this guy, but he was older than me, and quite more experienced. I knew better than to fall for him because he was busy with other girls in his life, so I stuck with being just friends. And over time we became best friends. Like I know everything about him and he knows everything about me, love life and all. And I'll just add, that this guy is not some asshole or anything, he is a sweetheart that actually genuinely cares, and that's why we are friends. So later in the year, his gf left for college and I was being a good supportive friend as much as I could, because nothing like this has ever happened to me, and I've never been in a relationship before. And I guess while he wasn't busy with other girls it gave us time to get close to each other. We go to the same school, but at school we try not to give off the impression that we are together or anything, cuz people like to make stuff up and see things that aren't really there. right? so we keep the close things to a minimum. Lately he has been stressing out with college and things, so sometimes we hang out in order to relieve stress. we enjoy cuddling with each other, and just holding each other and being in each other's presence, but there was never this romantic feelings or anything, until one time we were hanging out and he was testing the waters a bit, and he kissed me, i told him, we shouldn't kiss, because we're just friends, but later that time, we did some more romantic type cuddling, which we were both comfortable with, because we are complete best friends. well that was just the beginning, the next time we hung out, I went over to his house and we "watched" a movie. well it started with cuddling, and then it went to kissing, and then his hands wandered for my boobs, which i was okay with. then we talked some, and we told each other how we felt about this. we agreed that we don't want a relationship out of each other, but we were questioning if this was okay for our friendship. we both didn't know the answer, so we persued it. later in the evening his hands wandered lower and we got to third base. this was new to me, but not to him, the only thing that was new to him was the whole FWB idea. never done that before. and a relationship is not something that we have in mind because we would be a wierd couple. (im taller and younger, and hes shorter and older). and well now everytime we see each other we cuddle and hug, because hes going through a rough time, and im there for him, in any way he needs me. he has never really showed any relationship interest in me, but now im not so sure. I've noticed that he flirts with me more often, and when we went to the movies, after he kissed me, like casually, like "thanks for comin" type-thing. and as for me, i'm not saying that i like him, for the time being ive tried to not be so clingy, not crushing on him, or anything, but still showing him that i care for him and do have feelings for him, that are more in a loving friendship type. but at the same time, loving him in a relationship way would not be hard at all. we've been telling each other things like "im really glad you're in my life" "im so lucky to have you" and IMing each other smiles and :* but im not quite sure what that means. we can't be in a relationship now because he's going to college, starting the summer, and we just want to spend as much time with each other as possible. Should we continue we this loving type relationship, or just stop, go all the way? thoughts?