"Right now I am struggling with a lot of anger and bitterness and it's hard for me to find a positive or constructive perspective on it"
Grieving the grief; for me and as I've heard others share, involved anger and bitterness. For me it involved an awful lot of pain and misery to even reach the anger and bitterness stage. But reach it I did and pass through (much) of it...
Without wishing to appear to be minimising your experience... its all part of the process and as long as you don't get stuck, perhaps like me, you'll look back at that anger and be glad you didn't keep it stuffed down any longer than necessary.
Wretched really... the only way through much of this ****, as far as I can make out, is to suffer from all the pain and shame that's been locked away. It's like cleaning (unwanted) graffiti off a wall, each bit is hard work and mostly unpleasant, but done slowly enough, bit by bit the wall gets cleaner, neater and better and easier & as the progress becomes apparent... the positives become obvious to all.
Take it easy...