Constantly coming out is hard. At least 2 years (possibly 3) since I was forced to come out as bi and poly to parents, they still refuse to acknowledge (let alone accept) my relationships. They still pointedly refer to partners as 'your FRIEND'. Every time they purposefully do this, I have to firmly "remind" them that we're partners. They never ask after them. When meeting them they barely even acknowledge them, which really hurts me, and doesn't exactly make partners feel great either.
If someone you love is queer or poly, it's not your place to agree or disagree with their relationship. They're an adult and have a right to love whoever they want. You either accept them with all your heart, or you don't. If you don't, you're choosing to close your heart to the joy their partner(s) brings to their life because they offend your sensibilities or make you uncomfortable. You're telling them that your comfort is more important than their happiness.
As long as you think the problem is with their orientation/relationship and they think the problem is you not accepting them, you'll be driving a wedge between you. You're making your love conditional on them being a different person. Whether or not their relationship/orientation is fixed forever or changes, the horrible feeling that your love is conditional could outlive all of it.
My partners' commitment to me is not contingent on my loving others less than them. It's a level of love and commitment I could never get in a monogamous relationship. This is fundamental, and makes me feel safe, secure, loved, and cherished.
