I have had three girlfriends since I was 14. I was engaged to the first, just played house with the second and married the third. All three are bisexual, although the first came out 50 years later as a lesbian. All I know are bisexual woman. Never had a straight girlfriend in my life.
However, no one ever knew about it. Saw no reason to tell anyone as we never felt guilty about it. If asked we would have told the truth but usually no one would ask why your g/f hangs out with her girlfriend. Our g/f lived half her time in our house for 38 years and no one thought anything of it.
The first and the last, my wife, shared their girlfriends so that we both loved her. That prevented any problems. My second g/f spent her weekends with her girlfriend and I never even met her. Maybe that is why we did not last long. I see a difference between a poly and open relationship. An open relationship is where both partners can date whomever they want or at least date with certain limitations. A poly relationship in my day and age was living life with more than one partner as a family unit where all parties loved one another and shared in not only the fun sex stuff, but the mundane day to day tasks that we all do as part of our lives.
Never saw an open relationship last long, to tell the truth. Usually one partner falls in love with their lover and gets divorced. As humans, we are hard wired to form emotional bonds with our sex partners plus spending time having sex and fun with one person and living with someone that has to do the boring stuff with you as well, tends to make you like the fun person better. She is not going to nag you to do household chores, etc..
All too often, open relationships are started to try to save an unhappy marriage. That is the wrong time to do that and yet, I saw it happen many times. I am sure that there are many who have successful open relationships but I have never found any couple who did that and is still married as long as we are. 45 years with a poly relationship where we only had sex with others as a couple, never alone. We really never dated. We wife swapped with friends and brought a friend into our marriage without dating them first.
Maybe you too should take a break from each other to sort out your lives. I lost my first fiancée because she was sexually confused. It would have been better if she told me before I invested my time, money and love in her.