Well, I think it's only natural to worry about the future. Most of us do it. Bad things can happen in the future. But if you agonize over it too much, you kind of rob yourself of the happiness you could have enjoyed here in the present. Not to mention a whole lot of the bad events you fear/anticipate in the future may never come to pass. The only exception would be when you got so hung up with "doom and gloom," that it caused you to act as if all the bad stuff was already happening, and that can make M feel pushed away. So try to avoid that part of the vicious cycle.
You'll definitely benefit from having things to do that you enjoy while M is away. Something so it doesn't have to be "scary to be left alone with your own thoughts." Your thoughts are trying to scare you. Shoo them away with TEA exercises, visits with friends, and fun stuff that you like to do. Then you won't be in "freak-out mode" when M shows up; you'll be in a healthy/positive frame of mind. Above all, seek to appreciate and enjoy what you have right here and now, rather than agonizing over all the many things that could go wrong tomorrow. You couldn't possibly cover everything that could go wrong, and in the meantime you're missing out on the hopeful feelings about the many things that could go well tomorrow.
If there's anything you can do to prepare for the future, that's a good idea because it might mean better odds of things going better. Just don't obsess so much about preparing for the future that you actually barricade yourself against the future, both good and bad scenarios. When preparing for the future, prepare yourself to receive the good things that will happen as well.
More practice and thinking will get you in a little better cycle, as time goes on. I think that's something to look forward to.
Love means never having to say, "Put down that meat cleaver!"