Welcome to the forum!
I appreciate the sensitive and difficult nature of the stuff you are going through.
Let me see if I can sum up what is going on in my own words, to make sure I understand it.
You have a mate and have struggled with your relationship due to a bunch of mental and physical issues, including your sexual activity level which does not match hers. You have been working on yourself and feel like you have been making some good progress, but you still do not feel that you are satisfying your mate.
You are feeling like one way to take the pressure off you and to get your mate the sex that she wants is to allow her to have other relationships, in addition to the one with you.
Have I summed that up accurately, or have I totally missed the boat on something?
"Listen, or your tongue will make you deaf." - Native American Proverb