I've NC for this but I have been on MN for a while and I could really use some advice. I came out of a long term relationship about a year ago and then in July I met someone online. We have really clicked and he's absolutely lovely so all that is fine. Except... and this is where I need the advice as I don't know if I'm being stupid or if it really is an issue.
He has had 3 major relationships (never married but has a child from the last relationship, this is all fine and absolutely not the issue). The thing that is weighing on my mind is his feelings about his ex from the first of those relationships, which was almost 20 years ago now for context. He has variously described this ex as his 'first great love' and the love of his life (as in 'I met the love of my life at...') when we were discussing relationship history. He blames himself for their break up, it was caused by issues he had at the time, she subsequently cheated on him and it all clearly devastated him at the time.
I am obviously aware that everyone has a past, my issue here is that I don't know if he ever really has or ever really will get over this person, and I don't want to be anyone's consolation prize. I know they are not in regular contact, and are possibly not in contact at all, but in another conversation a month or so ago he said kind of in passing when talking about something else 'oh (ex) pops up every few years and puts me off my stride for a few days' - tbh I'm not sure if he meant that she literally gets in contact or if she pops up in his head, but either way, I don't really know how to take it. What precipitated this thread though is that he is moving house and last night I saw something (a trinket type thing) and asked him where he got it and it transpired that she gave it to him the day they split up and he has kept it ever since. It was obvious that it is important to him; as the conversation went, he said 'I have no other memento of it' (relationship) to which I asked 'do you need one?' and he replied 'yes, it was very special to me'. He has obviously had this thing as a treasured possession for nearly 20 years now and it still means a lot to him. It was one of the first things he'd brought to the new house and I'd actually been handed it to hold in the car when he was loading his stuff in (it's breakable) prior to me asking where he'd got it.
I let it go after that, he put it away out of sight (not prompted by me), and he was his usual lovely self, but it's been weighing heavily on my mind ever since... I obviously have past relationships and one in particular was very special, but this (the way he talks about it) just feels different. I know he and I haven't been together long but if it hasn't changed by now maybe it never will? What if she suddenly 'popped up' 6 months or 6 years or 16 years down the line and said she wanted him back, would it be no contest? Will she always be the one (that got away)? Will he always deep down be regretting that he's not with her and wishing that he was? Or am I being ridiculous and precious and over sensitive by feeling that I don't want to be "second best" (for want of a better way to put it)? These are the questions going round in my head and I honestly don't know. Should I talk to him about it or am I making an issue out of something that isn't an issue? 
Sorry, I didn't mean this to be so long, brevity is clearly not my strong point.