Hi Wells,
Yes, what you're going through is really hard. But don't romanticize the past. You told us about it, and it was not healthy or fulfilling. The only unambiguously good part was the dog, right?
So . . . how about doing a short term dog rescue so you have a new canine companion for awhile, until you're ready to adopt one for real? Or a house rabbit? The animal rescue organizations in my town are always looking for short-term rescuers. I think a new friend to take your mind off the ex might be really good for you, and I'm sure there is an animal out there who really needs you.
Hugs--