He’s jealous of the other guy. He obviously has a problem with the fact that you’ve moved on, and he is now just an ex-boyfriend.
That’s why he wants to know the details about your life to find out whether you still have feelings for him or not.
His jealousy will probably make him trash your new boyfriend.
It could be only that or he really misses you and wants you back. Otherwise, why would he express any feelings upon finding out you’re dating again?