I feel ya. I used to go to Jazzercise religiously until I started dating DH, then I gradually started to slack off.
I was the same way about working out when my marriage to ex-dh sucked: I think it was a way for me to release the tension and resentment, plus it got me away from him for a period of time.
I think you have different priorities which is why it's slacked off. But fear not...you can get back into it. You'll feel better and it sure helps with feeling good about yourself when your clothes fit better. lol
"Why would you ruin perfectly good peanuts by adding candy corn? That's like saying hey, I have these awesome nachos, guess I better add some dryer lint." - Nonny
When I run out of motivation I also like to mix it up. For me that usually means signing up for a class - which will make me show up since I can't miss a class (overachieving HS student here). Going to whatever class it is gets me off my butt and into the gym where I usually stay for an extra half hour or so on the machines.
I have felt the same way as of late. The only thing that pushes me to do anything, is how good it feels after I'm showered and curled up with my kindle. That is my whole motivation these days....how good doing nothing feels when I am done.