You mention that your boyfriend uses weed. Weed lowers testosterone, which can also contribute to depression and lower sex drive. Maybe the weed is effecting him or maybe not. I can't be sure. But maybe it's a contributing factor. And, of course, it's up to him if he'd like to stop using weed to see if it would improve his outlook.
First of all it is important to know that you are human and u can only be so supportive, getting frustrated is apart of life it doesnt mean that you are a bad person or a bad girlfriend. Depression robs you of so much pleasures in life, even the ones that used to feel good. The disconnection that your boyfriend feels is not your fault or anything that you have done or didnt do, it's how the condition operates, it takes away our joy and alienates the one we love. However, you two may communicate about doing various things and activities that may help bring you closer and put some spice back into your life. If his meds are not working the way they should, then he should speak to his doctor as well as continue to go to therapy. It may not seems to working but ut takes time, it doesnt get solved overnight. Try as best as you can to continue being supportive, if he is adamant that he still wants to move out then let him. It makes no sense to hang onto someone that doesnt want to be there. It would make him more depressed actually, feeling trapped and trying to be comfortable with the living arrangements when he is not. He may need some space. If he decides to go take some time for you because often we spend so much of our time trying to fix someone else's problems that we forget about us. Remember you're important too.
I hope it all works out for you. Keep in touch.
Anna~