Hi PhysicsNerd,
Welcome and hello

It does sound like he struggles to regulate his emotions. There are skills to help deal with emotional arousal and this is a great place to work through those skills. It also sounds like you have the ability to look at your own actions -- this can be hard for some people to do.
One skill that can escalate things is what people here refer to as JADE (justify, argue, defend, explain). When someone with BPD is in an emotional dysregulation, JADE-ing tends to escalate those feelings further. It's a natural defense mechanism to defend ourselves when accused. Many of us have had to learn ninja skills to communicate in ways that de-escalate situations.
The lessons to the right (lesson 3) has helpful material on validation and SET statements (support, empathy, truth) that can help.
Are you staying with your BF at the moment? Or taking some time to regroup?
LnL