I want my boyfriend to move out but afraid of his reaction?

It's fine if you need to do this for your own health, which it sounds like you really need to do. It sounds like he also needs to focus on himself. You might break up over it, but you might break up anyway. Recovery from bad depressive swings (and codependence) tends to involve the sort of identity makeover that leaves you wondering why you stayed together as long as you did and not really wanting to be together anymore. It might not turn out that way, but it probably will. But staying together isn't doing anybody any favors right now so you should try something. So, no, you don't get any special guarantees that you'll stay together (healthily) if you do this. Don't make "temporary" arrangements that are not financially viable permanently. Plan for failure, hope for success.

You can't let the fear of how someone else is going to feel keep you captive in a relationship that you don't want. It's not fair to either one of you.

Being honest is the best thing you can be when being in any relationship. He could either react negatively or positively but you will never know until you do it. No matter what his reaction is, you can get through it.

Dealing with this might be difficult as you create so many different scenarios in your head, but you never truly know how it'll go until you have a mature talk about it in a comfortable setting. Whether you may have a strong connection with your boyfriend or not it is always best to communicate with each other rather than leaving words unsaid in the open air. If something may be bothering you do not hesitate to speak upon it because hiding how you feel or what you would like to say just might eat you up inside. If you receive a reaction that you are not hoping for do not stress about it or let it worry you, find a way to move forward from that moment.