You will never be able to get him help if he doesnt want it.. If he chooses to not seek medical attention and Therapy to help him work through whatever roadblocks its causing in his life well then you have a choice to make...

You can continue to be part of the off and on communication or you can just let it go and realize you deserve someone that will be emotionally there for you and have a healthy relationship with.

Depression can make a relationship hard at times, but relationships regardless of mental illness or not all take work and communication to really be healthy for both people.

Good luck and welcome to PC