Is it fair of me to tell an ex that the time I spent with her was the happiest I've ever been?

I dated this girl years ago (ie. the 1990s) and since we split I have thought about her on a fairly consistent basis. With social media, etc. we reconnected several years ago and I have had the urge to reach out to tell her that, while I regret not fighting harder to stay together, I truly appreciate the time we spent together. While I was with her was literally the best time of my life

We have both moved on with our lives, so I am in a conundrum as to whether it would be fair of me to drop that on her, or am I being selfish and trying to get closure on that part of my life?

Is it fair of me to tell an ex that the time I spent with her was the happiest I've ever been?
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