Single vs Couple

Heh, it's rare for me to ask for advice around here, but this is actually one topic I can't ask my friend, since it's about them.

If I were to name my 6 closest friends, a year ago 4 of them would've been single like me. Now I'm the only single one left, and it kinda sucks. A few of them are dating each other, which means I get to lose two single friends in one go instead of one, and when they fight I'm stuck trying to stay neutral.

It's depressing, really. 3 of those close friends are guys - now I'm that person that makes you nervous because I'm a close friend of your boyfriend/girlfriend from before he/she knew you. We used to all go out and just get hammered and have loads of fun, now it's hard to convince them to go out instead of checking out a movie with the gf/bf.

In general, my six favorite people have suddenly become far less available to me. We all still have fun together when we do hang out - but it's only like old times when their boyfriend/girlfriend isn't around.

I'm not too good with relationships myself, and I love my single life, but it's starting to get a bit lonely. Don't get me wrong - I know lots of other people that I can call to hang out with - but I still really feel the hole those six used to fill.

I'm starting to wonder if it's really possible to maintain a close friendship with couples, especially the opposite sex member. I feel like I'm slowly losing these people to each other and it's been really hard on me.

So, thoughts?