You are doing all you can, it is not your place to be a punching bag when your friend's Mood dips. If he is not taking Therapy seriously and has stopped necessary meds then he is placing a great burden on you, unfairly imo.

Lashing out in anger or frustration can be a sign of Depression, but that does not excuse it. It should be worked out in Therapy, not on a friend's shoulders.

For me, to be a better friend I would suggest you try to pursuade him to return to prescribed treatment and then set ground rules for the support you are able to offer him.

Above all else, do put your own welfare first.

Dave.