Hey Saturneptune. Hope you're having a great Fourth!!!
Great question.
I believe Scripture says that the marriage bed is undefiled, meaning two married people can do whatever together. But that doesn't mean they can't defile it by bringing in someone or something that isn't supposed to be there.
They can still lust or try to add another person, etc. Those things are definitely sinful within the context of marriage.
That's how I explain it to couples who say it's okay for them to watch porn TOGETHER and that it's okay because they are married.
The marriage covenant with God does not give two people the right to sin against God.
Do yopu agree with paul that homosexual acts are a persion of the intended order, an unnartural act, against what God created and means to be the "normal and correct" way?