Do you have to know the reason why when someone you care about deeply acts like you're nothing?

We’ve had a gazillion questions about how to get over a lost love. This, I hope, is a little different. I’m wondering who needs to know the reason why someone hates them?

This always tends to trip me up. There are times when I just can’t figure out why someone is acting the way they are acting. It gets me crazy, and I can’t let go of it until I get an explanation. The longer I go without an explanation, the crazier I get. If one is not forthcoming, I just don’t know what to do with myself.

Anyone else out there like this? Or can you just drop someone with no explanation needed? Do you want to know why? Or can you let it go, just figuring the relationship is over? What do you do if you don’t want to let it go?