Welcome JS. I am sorry to hear you are struggling. The people here are very thoughtful and if you wish to ask for advice you can post in the Relationships area they will do their best to listen and advise. It makes things easier to follow if you give yourself andd others nicknames, otherwise we see a confusing stream of M's, DH's, B's, etc.
If you have not already you should try the search function and you will likely find discussions of situations similar to your own.
We have all had struggles and can sympathize. There are people here who are monogamous themselves in addition to people in all variations of ethically non-monogamous relationships.
Leetah