There is a part of our brains that reacts to change in our routines as if it was a threat. All you can do is step back a little bit from your emotions and try to see things logically. You've discussed this with him and have been expecting it. Remind yourself that you are not in danger. Occupy your mind with other tasks, and seek out the company of other loving people. Those thoughts will likely still surface, but you don't need to pay attention to them, and it could be uncomfortable for a while but that won't kill you. Just breathe, treat yourself well, and try to engage the more logical, rational side of yourself so you can see things more clearly and without attaching upsetting emotions to it all.
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein