Honestly, when I first quit, I was in a conundrum. That's why it took me multiple times to quit for good. It's also the same reason I get hooked on a show or movie and when it ends I just can't deal with it.
Basically, I get stuck in characters and situations. I was so used to the world set up in FFXI that it was hard to adjust being away from it. I mean, I had a life, too. I was going to school and hanging out with friends and whatnot, but the game was sort of my rock.
What I've found is that you need to occupy your time with other things. Even when you hate it and you think it's not worth putting your time into it, keep at it anyway. For me, that came with being more social, exercising on a regular basis and stuffing my nose in books. Just like any addiction, it's hard to deal with anything else.
If anything, try to remember what you enjoyed doing before you started playing FFXI. I know it's been around for a decade and a half, but surely you're older than the game is. If not, well... go discover the world! Odds are you have, though. Thank back to those activities and see if you could do them, again.
Also, yeah. Be more social. One thing that bothers me about technology these days is that it's too easy to get sucked in and not experience all the great things life has to offer.
So, like the posters before me, get off your keister and live a little. If you don't like the activity, push yourself to try it anyway. Start playing a new instrument. Get lost in the works of Shakespeare or Coleridge. Go see what's so important about that big yellow ball in the sky.
Edit: Like my buddy always told me, if we had spent the time playing games studying and working on our education, we'd probably all be doctors by now.