I also have some things to add on the topic of idealization. People with BPD tend to idealize people—that is, to see a person as all good or all bad. Your boyfriend might see you as the most amazing person he’s ever met, someone truly perfect in every way.
To some extent this is normal, to idealize your significant other. The difference is that for most people there is an element of choice in it—we idealize our significant other because we want to, because we’re willing to let go, to suspend disbelief. Deep down in our hearts we know that the other person is not perfect, but we’re willing to let the truth slide for the sake of love.
However, for the person with BPD this is not a choice. Your boyfriend is not trying to idealize you; he can’t help it. This also means that his opinion of you can fall curiously fast, because it doesn’t have the normal element of will to it. It is impossible for anyone to be passionate about their SO all the time; but for most people, a sense of dedication can take over when the passion fails. But for someone with BPD, they tend to get carried along by the wave of their emotions, alternating between delirious love and overwhelming apathy or hatred.
There are two things here. The first is that you need to keep your head above water a little bit. You need to know that you’re not really the best person he’s ever met—you’re just someone who hasn’t left him yet. You’re not different than the others, you don’t see him in a way that no one else saw; you’re not somehow able to see the real person in him that everyone else missed, and you’re no better able to deal with his emotional turbulence.
Don’t be afraid of showing the real you and spoiling his idealization. On the other hand, know that that is exactly what he fears the most. When he leaves you for good, he’ll say, “it turns out you were just like all the others.” And he’ll be right—you’re a real person, just like everyone else he’s ever broken up with, but if he’s going to be in a relationship he has no choice but for it to be with a real person.
The second thing is that you’re going to have to get through the low points. There will be weeks, maybe even entire months, where he will seem apathetic towards you. You may find that the only thing you can do is to be apathetic towards him back. Understand that this will become the nature of your relationship. You can’t have a relationship with him that is passionate all the time. If you feel that a relationship filled with long, apparently random stretches of apathy is not right for you, then he is not the guy for you.
There will be times when he seems to doubt everything you say. He will seem to resent the sight of you. Looking into his eyes will seems strangely tense. That’s a feature you are going to need to live with.
You will develop a tough skin. He will criticize you constantly, but seem to be unable to take criticism himself. It’s ok to get on his case about that. If you point it out to him, he will listen. Begrudgingly, yes, but he will listen.
He might hit you. He might tear you down verbally. He might cheat on you. If these things are show-stoppers for you, you might want to leave now. But he’ll also love you intensely and there will be many good times. Not unlike a normal relationship, just a little more intense.