How do you accept the things you cannot change?

trying to stop being so thin skinned:

I had an online discussion with a random, we had a short but intense exchange until he replied and then blocked me, robbing me of a chance to reply.

I feel hurt because I couldn't reply. To me that means he won. I feel insulted and angry.

Yes, this is something I should talk to about with a shrink, but the therapist I contacted hasn't replied yet, so I might have to start looking for a new one if this one ain't reliable.

In the meantime I turn to the second best thing I can think of: this channel.

I can try to rationalize it: I cannot change it, I'm letting that guy live free in my mind, letting it go is the rational thing to do.

Except that here I'm not being rational, but emotional and I don't know why this triggers me so much.

Not getting the last word triggers me. How would you solve this?