Is it normal to have the one ex who you're just not over?

[DamianGrammaticus]

I don't even think that ex is the right word- we had a short fling, about five years ago and it didn't work out for so many reasons.

I wasn't particularly heartbroken at the time but his photo randomly popped up through a friend of a friend on FB yesterday and it was like a whomph in my heart.

I can't believe how stupid I'm being

It is like on Bullseye when they used to bring in the speedboat at the end and Jim would say "Have a look at what you could have won"
You think of this lovely imaginary future you could have had with your boat, totally overlooking that you get seasick and live in Tamworth.

For some people I'm sure it is. For many others it isn't. I don't think there is one answer to this.

Yes, commonly known as 'the one that got away'.
But I agree with pp, it's often just unrealistic expectations of what could have been, not what it actually was.