Oh love, anything I say will be insuficient I know, but I can't read and not post.
Your X is callous to the extreme, I don't know how you do it, but you have to disengage from him, he is no use to you at all and will actually bring you down.
Have you had bereavement counselling? I can't even bear to think of how it is to lose a child, the very thought of it has me in tears. I am so sorry that you lost your son in such dreadful and tragic circumstances.
Is there ANY way you can find a way to focus on YOU, focus on your youngest DS and live every day as it ought to be lived? Happily, for the sake of your eldest DS? I am sure he would hate to think that you are so miserable, I am sure he would want you to be happier. I know that it's an unreasonable idea for him to have, but you have to go on. Being sad is understandable, but you have another DS here, and he needs you to be strong, be hopeful and be there for him.
Your eldest DS, must have been in some hellish emotional turmoil to do what he did, please remember that this is not about you, it was nothing you did, this was an illness he had, that made him take drastic and deadly actions. I made an attempt on my life, many many years ago and my thoughts and feelings were all about me at the time, I thought no-one would care, I thought they were burdened by me, so it'd be better without me. I wasn't doing it for any failure of anyone else but myself. The thought of inflicting such pain and suffering on my entire family, and the extended family, as I know would be the case now rationally thinking literally horrifies me. Depression is a deadly disease. People forget that.
Talk to your youngest DS, talk it all out. suicide affects the family for generations, so it's important for everyone to try to get through and understand that they have to go on, without guilt, without blame and without fear.
I hope my words aren't too inadequate, my whole heart aches for you and your boys, I wish I could take the pain away from you all, I wish you could heal.
((((HUGS))))