Sometimes, some of us just want to be nice for the moment and there is nothing more that is expected. Lots of sentiment with ex's and we can remember the good times as well as the bad times. For the good memories, being nice with an ex and nothing more or expected is the whole exercise in itself. I may be talking for a minority of men though.
I was in Montpellier one time, and I was at the bus stop talking to a girl. We bumped into each other 30 minutes later and another quick chat. we said bye and made our way. I turned back and asked her if she wanted to have dinner with as I was going to have dinner anyway. She declined. So we parted, but she turned round and said "why not"? We had a lovely dinner and more conversation and then we said our goodbyes. It was for the moment because the initial conversation was good. Again, there may be no future but for the present it can be perfect. Now I feel sentimental again.