It is a tough situation for you. I ended a 20 "friendship" and it was not easy. Like you I was tired of being a sounding board and complaint dept.
Good luck, it will be difficult. You can do it.
Distance will help it end if you move to California. I still think of my old friend, now and then, but, I don't contact him.
I recently was in his area and didn't even bother to go by his place. It was a sad situation, ending the friendship.