What I need in moments like that isn't harshness and for the other person to pull back because they don't like how I'm treating them or they think I need some space. Instead I need them to try to connect with me, because in those moments where I'm either pulling away from others or lashing out at others that's just because I'm in so much pain and so frustrated and upset at myself that it's manifesting in counterproductive ways. I need that person to empathize with that pain and reassure me that they're still here for me, even if I'm not behaving in the most perfect way right now.

I think in absence of a (good enough) parent the only person who is willing to do that is a therapist. Most people will react rather than respond to bad behaviour.