Why can’t I do it by myself?!

I’ve had this problem for so long. I used to be able to get myself off and then all of a sudden I just wasn’t able to anymore and I have tried so many things and then if I don’t get off I feel disgusting and it’s so frustrating.

When having sex it’s great all is fine but I just can’t do it by myself and it’s so annoying cause I can’t have my SO here all the time

I need helpppp