I have nothing against practical monogamy save for this. You must free the ones you love before they can freely choose you.
It’s why insisting on lifetime guarantees of sole-possession is the worst possible way to soothe your jealousy or fear of abandonment.
If you can’t let go of that fear long enough to put someone else’s happiness first, it doesn’t matter how many oaths, contracts or incentives you use to fortify your conquest. You will never know what real trust feels like.