you are being used
I think you are wasting your time with this one, so move on and find someone who really wants your love and attention.
Poly is for people who often have a srong relationship but also like to play,like when they were single.
Having experienced being married and playing away,yes it`s great fun and makes you feel very young again but if it is only you that are having the fun,that is wrong.
If your partner wants to play away then ask him if you can too.Be blunt and watch for the fireworks when you ask to be equal.
Unfortunately it appears to me that some poly people like the control factor and that is not what poly is all about as it should be about being equal , accepting you can both meet and even sleep with whom you like.
Poly is really for very strong and confident minded people who ask no questions about each other and tell no lies.Unfortunately it often shows the chinks in your armour instead ie the relationship is not and never has been right.
So move on while you can !