I am in a similar situation and currently decoding how I feel about it all and what to do.
Started seeing him a few months after a LTR broke down (we have 2 kids). Was quite intense for 6 months or so. Then both of us started to get feelings and pulled away. he told me he met someone else he liked, I told him to get on with it and see. I saw other people in the 6 months after it stopped and we had hardly any communication.
Then in May time, it started up again, very cautiously at first, just sex pretty much and very little in between. 6 weeks agp it ramped up again, I was very stressed, just moved house and he helped me and looked after me a bit in the days I didn't have the kids (cooking for me etc). He started to come earlier, stay later, lots of cuddles and bonding.
Now I am in the position again I am starting to get feelings, he is too I think (this time form him he seems more emotionally involved in my life). I need to talk to him and see what he wants to do, but I think we either need to go public as a couple (and I am not sure I want to do this), carry on as we are and deal with the enivtable hurt when he pulls away again, or end it now.
Thing is, we have such a nice time together, I never want to talk about when we are together, and I don't really want it to end either.
Like others have said, you need to talk (so do I....) and see where it leads.