"Rejection sensitive dysphoria (RSD) is a condition that causes people to experience extreme emotional pain when they feel rejected, criticized, or fail. It's characterized by exaggerated reactions to rejection, such as:  

Having negative self-talk  

Having difficulty managing reactions  

Having a constant need for validation  

Adopting perfectionistic tendencies  

Feeling embarrassed or self-conscious  

Having low self-esteem and self-doubt  

Having sudden outbursts of emotions like anger, tears, and sadness  

RSD is often found in neurodivergent individuals, such as those with ADHD and Autism Spectrum Disorder. Some experts suspect that RSD is caused by differences in brain structure that make it difficult to regulate rejection-related emotions."

Here's where I disagree with the (some )experts. I may not be an expert, but I know what I know. And what I know, as the cause, at the source is: the sense of disconnect and not belonging. Belongingness...at the source.

"Belongingness is the human emotional need to be an accepted member of a group. Whether it is family, friends, co-workers, a religion, or something else, some people tend to have an 'inherent' desire to belong and be an important part of something greater than themselves. This implies a relationship that is greater than simple acquaintance or familiarity."

This is the vital need. This is the "thing", or lack of, that causes RSD, not a difference in brain structure. 

I'm standing on that. I now see the pathway to reach my SO, despite her own self sabotaging ways that are preventing this from happening. Me too, for that matter. It's what I ultimately want and need from being with her. It's these insecure attachments and defenses standing in the way. Being accepted ( not inspite of ) but simply, for no other reason than "just because".