Are some women irreplaceable to some guys? Like some guys will forever remember a certain woman?

I’m dating a guy who I think still is in love with his ex who he dated a couple years ago. They only dated for maybe 8 months but he still is in love with her despite having not seen her for two years besides social media. He recently told me he is going on a trip and it’s her hometown city where she lives and now I just wonder if he is trying to see her. I have reasons why I think he still is in love with her but it’s too long to write here and I’m lazy, but I know he does.
Are some women irreplaceable to some guys? Like some guys will forever remember a certain woman?
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