This is where people start to ask themselves if it's still slash. Occasionally they ask me, because I wrote a long story where Our Boys didn't get any physical satisfaction. And my answer is, hell yes. To me, the defining factor isn't whether they do it, it's whether they want to do it. To my mind, it's either slash or it isn't.
Sex is good.
In character sex is better. No sex is fine, too. Slash is not defined by the smut factor. UST is a powerful tool in the right hands. No one has to doubt the intensity of the characters' feelings just because they aren't expressing those feelings physically.