Hey Jealousy

Tell me do you think it'd be alright
If I could just crash here tonight
You can see I'm in no shape for drivin'
And anyway I 've got no place to go

And you know it might not be that bad
You were the best I ever had
If I hadn't blown the whole thing years ago
I might not be alone

Remember that song? I used to love it. Described a relationship I had at the time to a T. But I never really got the "Jealousy" refrain. Why is it about jealousy? Seems to me that it's more about regret.

I don't understand jealousy. Even when I experience it, I don't understand it. Either you trust or you don't, right? Either you're told the truth or you leave. Seems to be simple, but somehow it never is.