What does it mean when a guy show you pictures of his ex-gf?

So this guy I kinda have a crush on (he doesn't know) out of the blue while we were watching a movie showed me pictures of his ex-girlfriend and later that night we end up in same bed (though we didn't do anything, just a lot of touching, cuddling and almost kissing). Why would he show me pictures of his ex?
What does it mean when a guy show you pictures of his ex-gf?
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