Masturbation/mental health

This will be a lot. It’s hard to explain. So, I don’t know if anyone else has this problem, but when I masturbate I feel guilt, shame, feel bad about myself and spiral. My girlfriend on the other hand does it and doesn’t feel any of that. I told her for me it is a combination of my religion and my past addiction to porn. When I masturbate now, I don’t even watch porn. It just happens or I think about her. So, how can I masturbate without it bothering me, or should I cut it out completely? It sounds silly but I feel as if she won’t be as sexual with me until I pick one or the other and figure it out. I want to masturbate but don’t want it to bother me mentally. I kinda wanna just feel the way she does if that makes sense, but for some reason it always bothers me a little. How can I fix that so I can give her a positive update and get on the same page? Is masturbating bad for mental health? If so could improve on that? I want it to feel like I’m not committing a sin or doing something wrong. I wanna feel good after not bad. I hope this all makes sense

I also worry if it’d affect me in the gym or my testosterone/muscle or motivation to workout or be productive. That’s another problem

kinda just looking for an opinion though on what to do or how to handle it. I would love to tell her I got over feeling that way, but I could use help on that