He isn't interested so why is he so interested?

I have a male friend who's family have been family friends since before I can remember, we are similar ages so grew up together and supported each other through school/college. We have never been in a relationship together but have been there for each other through break ups and things. We decided a long time ago that we did not want to risk what we had to be in a relationship, in case things went wrong and we fell out even though we did admit to certain feelings for each other (this was almost 5 years ago though).

Within the last 3 months things seem to have changed. We are still very close but now if I mention a guys name he will want to know who that guy is whilst before he would encourage me to date them and not ask questions. He will also tease me about a guy I used to like even though he knows I do not like him anymore. If I say anything about a date he will act like he isn't bothered and go quiet for hours (very unlike him) but I know that is his sign of jealousy

For someone who says he is not interested in me why is he so interested in me? I don't really understand what is happened.

He isn't interested so why is he so interested?
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