Boyfriend keeps talking about his exes

My boyfriend and I have been going out for a year now. At the start of the relationship we both talked a bit about our past relationships. I've always had pretty good partings with all my boyfriends but he's had a couple of bad breakups. Once we got that conversation out of the way I didn't really expect him to bring up the topic too often but unfortunately he does. I wouldn't consider myself a jealous person but I do think he obsesses over his exes a bit. He went out with one girl for about two years but when I started seeing him they'd broken up over a year ago. However, he seemed to carry a lot of baggage from that relationship and if there were any issues with our relationship he'd blame it on her (she attempted to cheat on him etc). That's over and done with now because I told him outright that I was a different person and didn't think it was fair that he was using a past relationship as an excuse. Anyways, even though that stopped he still brings up one of his other exes in conversation. Like we'll be walking down a street and he'll point to a house and tell me that he 'got with her there'. Or once we were talking about tattoos and I said something like I wouldn't mind having one on my thigh and he replied '(Ex-girlfriend) had one there and it looked really hot'. 90% of the time I just brush comments like this off because I don't want to come across as jealous and unreasonable. We've been going out for a year tonight so we decided to go out for dinner. He brought his exes up a couple of times during the day and it wasn't an issue with me. But then we get to the restaurant and fore-mentioned ex has started working there as a waitress! He got really flustered about it and I was kind of like 'stop making such a big deal about it'. He went out with this girl for six weeks and then it fizzled out. He spent the whole dinner being really awkward and looking over his shoulder. I guess it really upset me because we've been going out for a year and he was obsessing over a girl he went out with for six weeks about a year and a half ago. I want to have a conversation with him about it but he's leaving in a few days to do a masters in a different country and I don't want to spoil things. Advice?

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