For me, the acceptability of sexual behavior begins and ends with the phrase "consenting adults". Within that framework, people have all sort of preferences, and it isn't up to me to declare which ones are acceptable and which ones aren't.

As for marriage, the government has no business getting involved in anything other than the legal aspects. It's all about legal rights and responsibilities, and I should have the same rights and responsibilities as any other citizen of the US, regardless of my choice of partners. It really isn't any more complicated than that.