cant figure it out

how can i sometimes be so full of love and life, and other times like now all i can do is cry. why cant i just bury the past. why do memories have to last and last. and i have plenty of good ones why dont they come to mind, instead of this nightmare buried inside. will i ever be able to just enjoy life, and not ever have to worry about crumbling inside. i can be having a perfect day and then out of nowhere a single thought can shatter my day. a conversation about my dad or watching a young boy and his dad. talking to a single mom whos ex has nothing to do with their child can all just send me back to that shower where i was fighting for my life, or that cell where i was all alone beaten and cold, i know its sad a grown man feeling like that scared lil boy all over again but when it hits me there i am that lil boy and i dont know what to do. when i was younger it was get high and fight or a long line of one night stands, all sorts of things but nothing ever truly makes those feelings go away, meth deadens the pain until i start to come down then i have to use again i can be clean for 6 months and out of no where those thoughts and feelings start eating at me and i fight and i fight then the suicidal thoughts start to overwhelm me and thats when i normally use i just want to know that one day ill be able to stop those thoughts from destroying me but so far they still do