I've had snippets of almost happiness but i can never really enjoy them because i know the darkness is never far away and its always so much worse after a relatively OK day.
i know how that feels. in fact i remember even in the midst of my worst depression, i desperately wanted the pain go away, yet when moments of happiness came in i would literally panic and think depressing thoughts to bring myself down. while it's still like that for me, it's only somewhat.
when you say you can never enjoy snippets of happiness because you know the darkness is never far away, do you experience that as anxiety like i do? a lot of the time, it's almost like it's the anxiety the thing that kills the joy in that regard, like my mind is constantly telling me, your happy now but your going to be depressed so don't enjoy it, then i become depressed, then i get depressed about being depressed.
I've been depressed for that long (20 years), will i even feel like me when i get better?
well as a person, your much more your depression. in other words, its something you have, not something you are, just as joyfulness doesn't completely define a person. of course things will be different though.
Is it even possible to get better after so long?
Will i notice the difference?
Yes and yes, just like life, its a journey to getting better with setbacks/accomplishments. and i imagine you gained a lot from the depression you've dealt with even though it may not seem like it. strong and courageous for one, as it takes both of those things to deal with those things, and i'd imagine you could be in a position to enjoy happiness more than the average person, who usually takes it for granted.
also, these books have very much helped with my depression and i recommend it for anyone, whether dealing with depression or not
http://www.amazon.com/The-Wisdom-Escape ... pd_sim_b_4http://www.amazon.com/Full-Catastrophe- ... phe+livingthis second one is about mindfulness
also this blog has helped me a lot
http://www.positivityblog.com/index.php ... -too-late/