OP I've re-read your posts and your OP reminds me that you're not really in a FWB situation. You're dating this person. As soon as you start seeing someone for things other than sex you're adding emotions to the mix (friendship or whatever) and I wonder whether this is part of your hesitation (it is a shallow friendship in that it probably won't last once you're done with him).
You mention "I'm not emotionally invested" as your first point of why you're happy dating this person, but I don't think it's true that you're not, I just think it's a different kind of invested, you like spending time with him, you enjoy his company, but you don't love him (which is fine of course). If you called him and he said "not tonight", would you be ticked off?
Based on your last post I'd say that you're almost totally happy where you are, but because of your legitimate concern that you're getting in too deep you're not totally happy... so I think you need to pull back a bit and stop spending non-sex time with him.
I truly believe you need to be happy with yourself before you can be happy with anyone else and it sounds like dating is definitely helping build you back up. And you can tell people that too. "I'm taking a time out from anything serious to focus on myself".
Why is the opposite of 'a relationship' meaningless sex? Why is the opposite of a LTR 'FWB'? I can't speak for the OP but personally, my experience of serial dating has been very varied and rich..... and has included several interesting and meaningful if shorter relationships rather than one long boring partnership!
Cogito, your query goes both ways. Why does the opposite of "several interesting and meaningful shorter relationships" have to be "one long boring partnership"? [emphasis added] I'm also not sure why you think a LTR (long term relationship) opposite would be FWB...
You're projecting a little into my post that wasn't there. The OP herself used the term "proper relationship" and I was using her language. FWB is a relationship, though it is typically strictly sexual and the OP's relationship is not, and therein lies the risk for some people when that relationship ends, which is what I mentioned to the OP.