Bleck, my 18 yo son has a GF, they've been together for almost 3 years. She live 3 hours away, and now that's he's away at school, they see each other even less. I'm am impressed that they've been able to hold it together in spite of the changes in their lives.
However, during school breaks she is here with us, and he just HANGS on her every second, the poor girl! She is loving and generous but gee wiz, thwe rest of us don't RREALLY need to see that!!
So I say, Geez James, let the girl BREATHE already! Ahem, uh, you know there ARE other people in the ROOM! Good Lord, gives us a BREAK!
You can use humor, they'll get the hint. It's a learned skill to control like any other behavior I think.
:)