I lost my dad 2 years ago to cancer, only 64 years young, my grandad at 77 and gran at 77. Ive felt the way you do, and seriously thought of ending it because its too painful to go on but if I did do it, I know for a fact he'd be waiting on the other side to kick my arse!. What im trying to say is not one of the people you have lost would want you to do this, and id bet everything i have they wouldnt even want you to morn to the point of depression.
Theres nothing wrong with letting them go and living your life. I let my dad go so he can rest in peace. Every day I think of him but I dont let it take over me to the point he has to worry about me.
I hope this makes sense and maybe helps even in a small way