Hi Snuggles, while I really wouldn't want you to be feeling the way you are it is really good that you're recognising that and sharing it. Now I think that it's amazingly (!!!) caring of you to be thinking about effects on your family and friends if............considering all you're going through, and absolutely use that if it's all that's working for you right now, but I'd say it may help a little more to focus on you.
Gradually moving past/on from these feelings might come a little easier if you looked a bit more at how you deserve more, your fight for you, how you could have more, where recovery could take you rather than feeling a sense of almost obligation/responsibility to others.
I'd say that that obligation/responsibility is a whole lot to have "piled on you" when you're already finding it so hard, and maybe making coping even harder at times with the "guilt" (??) going on.
And maybe I'm wrong but with "yesterday he was only 22 so sad." it kind of tells me that you think life can be precious???? And with you at 51........I'm sure looking back really hard you can see some really precious times, things that have made you who you are underneath all of this/things that have made your life what it was/is if you can work through this depression and in that the possibility of more precious times. I don't know maybe that's real hard for you to be thinking right now but just a thought.
So maybe more about you Snuggles and getting the help you need?? Because you do deserve help, you do matter!!
Would it be possible to have your medication reviewed, to see your therapist a bit more at times, or maybe a helpline if you're really struggling???
And of course you know we're here for you too!!!

Alison