What good is living, if your presence have no impact on another human being

This is where I'm reaching out one of those memory box in my head and thinking about it.
The closest thing to the subject.

I remember when my ex-bf told me he wanted me back, one of the reasons he said was ; I've become
another person since I met you, you've changed a part of me, and I've changed for the better
person in me.

I was touched.
But it didn't make me stay.
I don't know why. It just felt that way.

If you bring out the best in someone even if he's not gonna be with you through the end, at least he can be the best for the next person / or the person he is in love with now, even if it's not you.