Have you done a lot of online dating?
I really relate to what you're saying. I too have had a number of good, lasting relationships, 4 years quite intense OLD -i'm mid 30s and want a family so took it seriously- but just not quite the one until (hopefully) last summer when I met my partner who is ace. Yet I keep reading into things and upsetting myself for nothing.
I think it's because of my experiences on OLD. Not all bad at all, looking back, but it was a long slog of chatting to then meeting strangers, nothing happening and going back to being strangers, or having a short fling but it feeling not quite right and then going back to nothing. And a few idiots in between. So, not necessarily great heartbreaks but an ongoing mill of my hopes getting raised and dashed, even when i learnt to keep my expectations in check.
I feel like it might take a while to fully relax from feeling like connections are transient.
What I have been doing, if I start getting worried about something, is to resolve to put it to the back of my mind, sleep on it, then reconsider the next day whether it was a problem. That is to say, not talking myself round if there is a real issue, but not getting worked up if in the light of day, it's nothing. Whether or not you were OLD, could you maybe try that? If something pings up, mentally note it, put it to one side then quickly assess if it's anything to worry about with a bit of distance?