That's slot to deal with, and sounds like you've done a wonderful job supporting him and yourself so far. The main thing about depression I feel is not being hard in yourself, so please don't go down that road, recognise you can only do so much, and then it's up to you boyfriend to do the rest, you eilll be ok as long as you remember that and continue to loook after yourself and have some fun in life, by you having a good time, you can then share your positive energy with him.
Sounds like right now your swamped in empathy with his feelings and mood. And I learned recently that empathy can drain us as we out ourself in the olthre persons shoes, but understanding gives us strength as we separate ourselves. You can love and support him and it will be ok, because you'll be stronger to cope.
Encourage your boyfriend to get help outside of you, e open with him if you can, softly a little info at a time, so that he understands how you feel but not all in one go. As your right, he probably will internally feel that he's to blame and feel worse , so be open but tell him little by little day by day, and follow up with some positives.
Not sure if you'll find this helpful, or if it is helpful m just what works fir people who support me, they were unsure how to help me abs I told them how, but I as the depressed person was still very aware of the affect I had on others and could see that they were drained..the two people that helped me during my pregnancy, but now they no exactly how . I lost a few people along the way as it's had work to stand by someone so low and seemingly negative, but everyone needs to look after the,selves too I get that.. and you definitely sound like you need to look after your self and your emotional and mental health too