confused, I think you are dealing with this like an angel!
A friend of mine has a DP with long standing depression, and she also seems to display great patience with her man. But I have to say, she does come to the point of telling him what is and isn't acceptable. Yes, he's depressed, but some things bring her to the end of her tether and she will basically let him know in no uncertain terms. She (and you!) also deserve consideration and deserve being treated with respect.
Obviously you are prepared to deal with alot because you understand that it comes from an illness, but you should NOT put up with and take everything. There are limits and I feel you should tell him strongly where these are, wherever you feel "That's it, I can't take that". With my friend, it's the interation with her children. She won't let him ignore them or shout at them - there is a certain level of interaction that they deserve from a parent who brought them into the world and she makes it clear to him that this is the case. If he literally can't do it, he goes to bed or another room to be alone.
It sounds harsh, but as your DS gets older I think maybe it will be your role to ensure the quality of interaction between them, as it will be really important to your child! And to ensure your DH has the insight to take himself off if he is dealing with him inappropriately.
I have to say, it does depend on personality as well I think as my friends DP is a loving, besotted dad underneath his depression, so he desperately wants to be the best dad he can.
btw, he takes St.John's Wort and swears by it, has your DH tried this?
I'd like to wish you the very best of luck with it all, and well done for coping with it all.