I dislike peoples condition that it is kept behind closed doors, as though what they do is any more depraved than what heterosexual people. If what you're trying to convey is a desire for them to keep there sexual exploits private, I would have thought that applies to all sexual relations, gay or straight. I would not more like a stranger to tell me about their partners carnal adventures is they were heterosexual. Unless you are immediately bound closely with said person it's something acquaintances don't generally discuss.
However if you mean general displays of public affection, such as kissing, holding hands, all the other things people do in relationships, I don't understand what the problem is. Love is love, no matter who it's with. When I see a couple of any gender assortment being romantic I'm generally filled with a good feeling about life, rather than revulsion at their lustful exploits. Seriously, the behind closed doors stuff is an unnecessary proviso. If my gay friends want to discuss their relationship with me, confided in me something personal, I would be as open to discussion and giving advice as I would my straight friends.
I have no problem with anyone's sexual orientation if you hadn't worked it out from this.
Minor disclaimer: One thing about any public display of affection will make it annoying for me. If they're being excessively verbose and moronic when I'm forced to be near them, say on a bus, I'll tell them to develop some vocabulary and grammar before they consider furthering the discussion... well maybe not so politely. I might just tell them to shut up >.>