…Or rather for one with me?

I've recently discovered TRP and RPW and have been soaking up all the awesome knowledge, but I couldn't really find anything to help me out with this question. If it's been covered before or if I'm in the wrong place, I'd be grateful if you could link me to the relevant post/relevant section!

I started dating this guy last month who was a natural RP (or maybe a secret TRP, who knows!), we had lots of things in common and I thought it was going great. Except three weeks in, I was basically dealt a soft next and have not heard from him since.

There's probably a few things I may have done wrong. Maybe I appeared too keen, or I gave in to sex too easily/early to keep his attention going afterwards, but what I can't really explain is his conduct.

I'd assume most guys looking for ONS go for the minimal effort:maximum reward approach and are general quite straightforward. This guy invited me for a couple of dates, but as he had health problems (recent surgery), invited me round to his for the next few dates. I was treated to homemade dinner a few times and a couple of films too, and it carried on even after we'd had sex.

The week during which he went back to work, the number of texts dropped considerably. I assumed that his job was keeping him busy, but he flaked on me when I asked if he'd be up for having coffee, and I never heard from him again after that.

Now my problem is that in my (possibly completely wrong) books, he seemed like a candidate for an LTR, as I don't really know many guys who'd go to those lengths just for sex, it seems a bit counter-productive. Eventually, maybe my personality didn't appeal to him, maybe he didn't find the sex so great (not much that could have been done with his health problem), but my real questions are: how could I have anticipated being given a miss? What could have I done to keep his interest?

Bonus question: would it even be worth trying to give it another shot? If yes, what's the best approach, if not, why not?

TL;DR: I thought everything was going well with this guy, he's now ignoring me - how can you tell that a guy would like an LTR with you?