Your conundrum is something that catches just about everyone at one time or another.
My husband & I, for instance, corresponded online for nearly a year before we even met. We were platonic friends for years after that. Eventually, his wife divorced him, & I was ready & waiting to pick up the pieces. We've been married 18 yrs come March.
I ended up acquiring a FWB a few years after I got married. Naturally, we had to more a little quicker, but we've "been together" for 12 yrs now.
Sometimes, you just have to "declare your hand" (to use a poker metaphor) & see how the relationship goes from there.
Unfortunately, Aspies can have a difficult time not only reading the other person's signals, but in broadcasting their own. (FWIW: I misread a potential FWB 4 years ago. Just found out about it this year when our paths just happened to cross one day. We're both kicking ourselves for not being more observant!)