Envy, generally speaking. It's the one emotion that everything else chips into. I'm envious of girls for being born girls, I'm envious of everyone who looks better, I'm envious of everyone who lives in a better country, I'm envious of everyone with a better family, I'm envious of everyone who has a better life, I'm envious of everyone who knows what happiness feels like, I'm envious of everyone who isn't on-edge 24/7, I'm envious of everyone who can trust other people, I'm envious of everyone who can connect to other people, I'm envious of everyone who has a future worth living for, etc. etc.
See? All my mental illnesses, trauma, dysphoria, every insecurity and negative feeling, all my sadness, all my hatred for myself and others, all wrapped into one handy little emotion! It always leads back to envy. It's my core.