I know...when you leave a job, one should be very careful not to burn your bridges behind you. You never know when you might have to work with someone again (or worse, they're your new manager) or you need their help.
But sometimes, you just can't help it. When I lost my last job, I have no doubt that my former manager wouldn't lift a finger to help me. We definitely didn't part on good terms. So, you shrug and let it go.
Sometimes, you *think* a bridge is burned, but you find out that the bridge is in relatively good shape. Several years ago, I ended up working as a contractor for a former manager. He wasn't one of my favorite managers, he used to be a bit of a nutcase. But, he did me a huge favor by giving me a very well paying contract job that lasted close to a year. I left when I found a direct employment job and boy, was he mad at me. He was trying to get me hired directly and by not waiting for that, he was furious.
I never kept in touch with him and figured that I never would. But recently, as part of my networking efforts, I reached out. And received an incredibly warm response. He praised my work and seemed very, very glad to hear from me. So, I've just added him to my reference list. Who knew?
Unfortunately, he doesn't have a job for me. And he's still a bit of an oddity. He seemed very interested in getting together for lunch, but when I tried to set up a meeting, he backed off. I dunno. But, it's OK. At least I know that there's one less burned bridge behind me.