Extreme guilt around masturbation

Every time I go to masturbate, I am filled with extreme guilt to the point where (at best) the mood is killed or (at worst) I have a panic attack.

Really the only time I can do it comfortably is with my fiancé or with his permission. He’s really supportive and encourages me to do it and even encourages porn. We’ve watched it together a few times.

I know that needing permission is not a kink thing. I used to feel guilty about pleasing myself when I was a teen. Then after that my ex would shame me and tell me I was gross. My ex also had a porn addiction and wouldnt touch me. All while shaming me.

So because of that I’m also uneasy about my fiancé watching porn. Like I know it’s just a tool. I know masturbation is just good feeling and not emotional attachment. When we watch together, it feels good. And we like the same thing. Couples enjoying each other. But I can’t get over the fear of being replaced. Especially when his sex drive is really low. I know he can’t help it, but it triggers me because of past trauma.

I just don’t know what to do do help. How do I stop feeling so guilty?