Roommate "Problems"

My roommate and his girlfriend (who also happens to be a friend of mine) have spent the past two months spending every waking moment together (well, when he's not at work and she's not in class).  It wouldn't be so bad, except they can't keep their hands off each other.  It's as if our living room has turned into a set for a soft-core porno (and it's my sofa, BTW).  I don't really care what other people do behind closed doors, but I'm sick of feeling confined to my room because I'm afraid of walking out there and interrupting something.  I pay to live here, too.  But, since they're both my friends, I don't really want to cause any problems.  What should I do?

Make sure she's +18 though!  You don't wanna end up like that teen that was sentenced to 2.3k years in prison do you?  Check out World News for the article.