H is probably worried about how you will react to talking about OW (it comes out with what you described above). If you act like you don't care, eventually he'll get more comfortable (as it looks like he could be doing). Then his thoughts are less concerned with how to hide it from you out of fear for how you might react and more about what he is actually doing with his life.
My H used to do this with me (have preconceived notions about how I would react regardless of whether it was true) when we were first dating. In fact I think it was our first "fight." He went to vegas for spring break. I called him one night and he said he was at a "loud bar." His friend later revealed that they were at a strip club. A seemingly key fact to leave out! He did it because he was afraid of how I would react instead of just saying it and letting me react to it. That's not healthy.
So long story short - if you act like it doesn't bother you, H will notice because a) it's different from how you reacted in the past and b) he'll realize he can be more open with you and c) he can face whatever emotions he has to deal with as consequences of his actions. Does that make sense?
