Even if you no longer have feelings for him, you must have at one time and they get stirred up (I don't mean that you feel things for him again, just that emotional memories come up) so I think it is normal especially when it involves someone else close to you.

I think we all have "logical" mental links to people... like seeing people we know and like or dislike... and then we also have "mysterious" emotional links that we can't always understand, when someone is close to us. So no matter what that "baggage" is it gets stirred up, and we know it "shouldn't" bother us, but in fact it does for reasons we may not completely understand. I think that is just the nature of the human mind. And when we suffer from depression, when stuff like that gets stirred up, the most negative aspects get magnified, the worst stuff and the worst feelings about ourselves.

I know I have people from my past, people I was never even in a relationship with but that I held deep feelings for, and whenever their name comes up I can feel the blood drain from my face. It is just an automatic reaction and I wish I could "let go" of the past more easily, because these are things that I no longer have any real-world connection to (people I don't have to deal with, etc.)