Wandering eye while with your SO

My boyfriend and I are in a long distance relationship and mid 40s. We've been together almost a year. I can say that it is the deepest love both of us have felt. A few months ago I thought I saw him double glance at an attractive girl walking by, meaning he turned his head to take a second look. I didn't say anything cause I wasn't sure and I'm not the type to cause drama needlessly so I let it go. Well a month ago he did it again, twice, while with me. He's not staring, but turning his head to take a second look and trying to be sly. I didn't say anything in the moment but eventually shared that it upset me. He apologized profusely and said that he had essentially grown up seeing this happen with friends and family so he didn't think anything of it, but now understands that it's hurtful.

Here's the thing, it's been a month and I'm still bothered by it. We had talked about marriage and now I don't want to have those conversations. I can say that I see him differently after it happened. Look, i understand we are human and are wired to look at attractive things. But to turn your head to take a second look while I'm by your side? Feel free to do it when I'm not there. Our time together is already limited due to it being a long distance relationship. You're a grown man, shouldn't you have a filter? Anyway, it bothers me that I can't let this go and I'm waiting for some kind of ah-ha moment to snap me out of it.