Ffs I typed this out amazingly and the page refreshed as I was proof reading! Typing again but I might miss things out 
brutal advise and honestly welcome...
Backstory: work colleague of 4+ years separated from his wife just over a year ago, moved into his own place 8 months ago. Sepeated on bad terms with her wanting to see other people and him not wanting that. She’s happily dating someone new, but from what I’ve overheard from conversations is making his life hell during the divorce. I’d not spoke to him much in work and only really on the work Facebook chat outside of it. I’d always been attracted to him, but of course he was married etc so there was no office flirting or even ‘banter’. All very professional.
Around October - November last year he sent me a message on Facebook outside the group chat, asking if he could take me on a date. It was very out of the blue and I turned him down politely, stating I didn’t really know him that well and I wasn’t sure the timing was right (due to his messy divorce). Other factors were in play in my own mind, such as the fact that he’s 15 years older than me and I assumed he was a new bachelor trying to score with someone younger (i’m in my mid 20’s).
From that though we began talking. Although he’d sometimes suggest dating again it never went further than a friendship but we really got to know each other and I really warmed up to him, as we had a lot in common and he’s a really great guy. Fast forward to theee months ago, during a work nights out I had a one night stand with him.
The morning after awkwardness we had an open chat, in which he again expressed he’d really like to date me, more so now that we really got to know one another, as I initially it was because he’d just been attracted to me. I was still somewhat reserved and instead suggested we just keep things casual instead, as I still had this nagging doubt that he’d get back together with his wife somehow. He agreed.
All seemed perfect really. We talked loads still, the hook ups were fun in that we would usually watch movies or chat for hours and it was exciting. It worked. We both agreed to not see other people whilst hooking up and to let the other know if we wanted to end it. It was mutual. Then I ruined it all by catching feelings around three weeks ago. It just hit me - I was beginning to really like this guy. Only at this point things had begun to change and I didn’t like the changes.
We had stopped talking all the time like we used to and unless I initiated chat the only time he messaged me was to arrange a hook up. Although we still had a nice time together, the late night chats etc all stopped and I missed those.
He used to suggest we do things, such as see a movie we both said we’d like to see at the cinema, or do something we had both never done (like bowling - yes, I’ve never done it!) but they always seemed like a joke to me, as I secretly knew we never would as he’d suggest them and then never mentioned them again.
I actually realised I was more invested when he began to pull away and I missed what went used to ‘have’ so to speak, which was really a sort of relationship looking back on it without the dating, because we used to talk so much. I took advice from my friends, which was to purposely not initiate chat, but I’d get radio silence until he was asking for a hook up. To me this suggests he’s no longer interested and why would he be? He’s had his cake and eaten it too.
In my eyes a casual hook up is only casual when there are no feelings involved. Me beginning to like him and him becoming so distant suggests to me he was never serious all along and that this needs to end before someone (let’s face it me) gets hurt in the long run.
So, AIBU to end this purely on the grounds that I don’t want to get hurt? If it ends now I’m confident we can resume a work colleague relationship and remain friends. It’s not like we’ve suggested this be anything more and quite honestly, he seems to like it like this and I don’t want to complicate things by pushing for something I initially rejected, when it’s obvious (at least to me) by his pulling away he never wanted more, not really. It’s clear to me this is what he wanted all along, no strings attached. Whilst I was up for this, as I’ve got to know him I’m beginning to want more.
(My original post was more fleshed out but I think I covered everything )