I guess that in a way, you are in a relationship but one that is more around what you need at this time of your life, without a "heavy commitment".
If you work so closly, sometimes behind "closed doors", coffee, emails,chats there would more likely to be "laughter" as well, discussions outside of work, and then there's sex.
It just may be that you can't cope with "a heavy relationship" one that involves living together, and acting as a "wife", cooking, cleaning, etc.
I am separated and i wasn't "ready" for at least 6 months to even date, but i have to admit, from the moment i separated, i was "ready" for that other she devil, only i refrained because well "reversal", i didn't want to get attached unless the guy was what i was looking for. And, if you are at all like me, then you want all that goes with it SEXUALLY, but not yet, that marriage component again.
Perhaps look at it differently then, for instance, i wouldn't live with my guy now, so i can be a bit "girly" again, and lust and desire him every day and have my space at the same time, but i entered a relationship and have that.
Maybe this "relationship", could still be a lot of fun and even more so, if you didn't have to even consider "next" and just went for now allowed it to be but on "mutually agreed terms" of where you are at in your life.
It is exciting for a man i think, when a woman spells it out that she finds him sexually sooooooooo, but at some stage, he has to feel like he's just a body with something attached that you want.
If he has fallen a bit, then he is saying, well i'm "cool" with the way it is but your an okay kind of "gal", so i enjoy talking with you and having coffee etc.
At this time of your life, with two unfortunate long standing relationships that sadly are no longer there, it is more than normal to not want to go down that path at the moment.
But, nothing wrong with going down a path you feel comfortable with except, sex only, is either on his side as a said, a body part in the end or he may like you.
The main thing is to understand relationships can grow as slow as you want, they don't have to be full on but they don't have to be overlooked either, there's more than "hot sex" like that hug when your really down....