Why do my boyfriend bring up his ex?

I met my boyfriend nearly a year ago, before that he had a 3 year long relationship that he ended and it was kind of on a bad note.
We both love eachother and I feel like we have really grown together and I've never been as comfortable with anyone as I am with him.
Occasionally in a situation that could be looked at as a negative one he brings up his past relationship. For instance; I tell my boyfriend that I hung out with a guy friend, he gets jealous and tells me he is bothered about it but he is glad that he told me and then adds that his ex wouldn't have done that. Or when he asks me to spend the night and I say "Sure!" he tells me he doesn't want to force me and then bring up his ex again.

This has happened a lot lately and I'm wondering why that is? Is this something I should be worried about or is it just a way for him to put things in perspective?

Why do my boyfriend bring up his ex?
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