At the time, i took the above outburst as a pure expression of distress. Now I am not so sure. Invoking self harm to demand or elicit a reaction from a partner is a pretty terrible thing, and the fact in the weeks after I was snappy, stressed or just wanted to hide and fall asleep when i saw uBPDx, and that this was characterised as me being 'horrible', is also awful.
Yes, it is awful to do what he did. It might help to separate the behavior from the motive. I don't know if we can know what a disordered person is thinking but we can decide, the behavior is awful.
I compare this to water safety courses I took at a teen. The lessons included being a possible lifeguard if we wanted to. The first lesson was to never let a drowing person grab on to you. We learned ways to avoid that and to get out of their grip if it happened.
Because a drowning person is frantic for air, and they will push you under and climb on top of you for air. It won't help the person either as actually, both people might go under.
Does this mean they are intentionally wanting to drown someone? Are they murderers? Probably not.
However, the result is, whatever their reason or intention, in this situation, they could drown someone.
Whatever reason your ex had for this- it was awful behavior. You can call it that, whether he was intentionally being awful or not.
I think we connect abusive behavior with the motive of intentional abuse, but sometimes it might not be intentional--
but it's still abusive behavior. I am sorry for the loss of your friend. I understand the feeling of wishing you could have done something. I think this is normal to feel this way. But I also think there was nothing you could have done, you had no idea this would happen.