Why is he giving me more attention now that he is dating her?

There is this guy that I've had sex with in the past. We are very close and there have been times I thought for sure he loved me. We can't be together as I am married (open relationship). Anyway recently he started dating someone. He says he is with her because he is lonely, but he is gonna give it a try. Since he has started trying with her he has been more attentive to me. Texting me more, asking to hang out, text goodnight almost nightly. I am just confused, is he just trying to make sure we don't lose our bond or is there something else?
Why is he giving me more attention now that he is dating her?
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