Ugh. I'm on the fence as to whether I ought to reply or not due to continued high emotions over the mess in my own life. So-take it with a grain of salt.
There is a limit to how far it is reasonable to limit your partner due to your own unmanaged insecurity. Insecurity is the responsibility FIRST of our self. Our partner can act as 'support staff' in our efforts to manage our issues, but they shouldn't be expected to quit being themself for extended periods of time due to our ongoing unresolved issues.
secretly dating more than one is cheating. Period.
Not communicating honestly and openly with partners AND metamours is a recipe for disaster. It is lying and dishonesty WILL destroy trust, increase insecurity and increase conflict.
In point of fact; it doesn't matter WHO is being dishonest with whom. Anyone who notices will lose trust. As you are experiencing in your awareness that she is lying to two other men AND you are lying to her which is increasing your dis-ease, distrust and general lack of comfort and security in the relationship.
I won't regale you with the long version. But, I have recently posted A LOT regarding metamours avoiding dealing with me AND lying in our dynamic. The damage of such actions is severe and I highly advise that you find a way to calmly and reasonably state to bith of them that dishonesty isn't going to ever result in healthy relationships, cheating has no place in poly and that while you are willing to work on yourself and support him in creating additional healthy, honest, up front relationships-anything including cheating and lying isn't in the cards.
Then-get real with yourself and define boundaries that allow him to create loving relationships IN SPITE of your ongoing fears. Feel free to look at our boundaries if you like-and check out Galagirls too. Outs very much address my husbands ongoing insecurities, while allowing me the freeedom to maintain my relationship with my live in boyfriend.
Be sure to include time limits for when you will re-address any boundaries that are strictly for allowing you a chance to work through grief or insecurity. Its not fair to just leave it open to 'whenever I feel comfortable' because you will never become comfortable until you face down the. Ir umstances and situations you fear and experience them working out.
"Love As Thou Wilt"