Can I masturbate after marriage if I'm not satisfied with my wife?

As-Salam-Wa-Laikum. I've a question related to masturbation. I know, Masturbation is Haram. But, here's my situation. I'm married for 23 years but for many years, I don't get excited for my wife and she also can't make me excited. She thinks, it's my part to make her ready and myself too. However, for many years, I forcefully make myself available to make her satisfy - **which is my duty**. But, I don't get satisfied and I don't get it done. I make myself cold forcefully without completing my satisfaction. My question is, ***is it permissible to do masturbation in such a situation*** (after making my wife satisfied, which make her tired and she can't take it anymore)? I need to do something to make my brain cold but I don't know what to do? I live in U.S. and I can't take a second wife nor do I want to divorce her.