I know to a certain extent that I shoudln't be analyzing what he says or trying to understand a depressed mind. But I just don't know if me being with him is good for him, or good for me anymore. I don't know what he is thinking. I wonder if he DOES want out of this relationship, but just doesn't want to say it. I wonder if he actually DOES want me to be there, but feels too guilty about holding me back. Or maybe a bit out of both?

Being at the end of this yoyo, has really stressed me out, and I don't know what to do about it.  I want to be part of his life, and i still want us to be together, if he is willing to work with me to find a way out of his miseray, but i have NO clue what is going on with all this back and forth anymore. Maybe he is just simply confused.
Hi LMS, I am sorry to hear you are going through a tough time.  I think you answered your own questions to some extent.  You are right, it is futile to try and apply logic or reason to someone who is thinking or behaving irrationally.  There is no way of knowing what stories or reasoning a depressed mind concocts.  As much as you can stop yourself from contemplating what he may or may not want, the better.  You won't know and his actions will send mixed messages (just as you are experiencing).  Instead you need to be in the uncomfortable space of paying attention to what *you* will and will not put up with.  Once you can determine what you will and will not tolerate, then you can communicate this to him.  You may find yourself saying "I'm not willing to ______", or "I refuse to _______" or "If this doesn't change then I need to _______".

You say that you "want to be part of his life... if he is willing to work [with you to find a way out of his misery]".  This is a good boundary to think about.  It sounds as though you want to stay with him IF he is willing to work on understanding (and managing) his feelings/behavior.  You could spend some time thinking about what the "working on" means to you, but I think you are very much on the right track of sorting out your limits.

Also, take care of yourself -- feed yourself with the little things that matter to you (a nice mug of good coffee/tea, a walk in the park, a glossy magazine, a chat with a good friend, etc), to help counter the stress you're feeling.