I'll try to give some possible explanations drawing from what I know about BPD, the ideas in the book "Controlling People", and the example I have with my BPD mother. This isn't to blame anyone but to examine some reasons and dynamics.
People with BPD tend to perceive themselves as victims. PwBPD have difficulty with uncomfortable emotions, and one of the hardest ones for them is shame. In victim perspective, victims aren't accountable. Issues are someone else's fault. This avoids shame. The example of your ex berating himself for not sending flowers- in a way, victimizing himself- being so hurt- was his way of absolving himself. Surely you would have compassion for him, rather than for him feeling he should have taken action.
The passivity in not taking initiative at realizing the moving in is temporary. He's dependent on you in terms of his living situation. He doesn't want to leave. By making you ask him to leave, you are the "bad guy" here and he would be victim, rather than to feel shame about depending on you.
One could also see these behaviors as somewhat manipulative.
One reason for people being controlling is that it helps handle anxiety. My BPD mother had very disabling anxiety and one way she managed that was to be controlling. She also was dependent in ways but to avoid feeling shame about that, she'd order people around. If everyone was predictable and under her control, she felt less anxious. However, to most people, this wasn't tolerable.
If people didn't do what she wanted, she'd react with angry rages. That we were fearful of upsetting her gave her control. So she learned that this was a way to control people with her anger, or, also her being very nice at times. She was manipulative but this wasn't about an evil or abusive motive, it was driven by her anxiety and her BPD. Still, the effect was the same- scary rages, verbal abuse. It was abusive- whatever her reasons or motives were. These relationships also can include a person being nice too. It's not all one way.
In these relationship dynamics, both people are controlling in their own way. When we are afraid of speaking up, or if we are walking on eggshells, in order to avoid the other person reacting- we are also controlling their emotions and reactions. This forms a double reinforcing situation. The pwBPD learns that their anger meets their needs in a way and the person who is enabling or walking on eggshells learns that this helps them avoid the pwBPD's reactions.
The book "Controlling People" does not specifically address BPD but it gives a model for the dynamic. The controlling person- whether emotionally wounded in childhood or disordered, turns to an imaginary emotional support which the author calls a "Teddy" like a Teddy bear is to a child, or possibly a real Teddy or toy during childhood. They attribute characterstics to the Teddy- Teddy does what they say, Teddy is there to soothe them. One could compare this to the idealization phase in a relationship with a pwBPD. Initually, to the pwBPD- this is the ideal person to solve their feelings, always loving, always attentive, always agreeing.
However, humans aren't Teddy's. Eventually a human has needs, or speaks up, or may say something the person doesn't like, or makes a mistake. At this point, the controlling person relives their wound, the Teddy has failed them. Bad Teddy- and the rage and anger comes out. Teddy must behave and get back into being Teddy.
This is not about blame, it's about identifying hurtful behavior, for our own selves. Your ex sounds like he has some emotional hurts, prior to meeting you. We can't repair these for anyone. They'd have to go through their own therapy to do so if they were willing. I think what is most helpful to you in identifying these behaviors is to not get into another similar relationship and be able to seek out people who will treat you decently.


