I'm reading "Sometimes I Act Crazy" right now and thought this passage might give you some comfort:
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"Trapped in a maze of inconsistent images, the borderline is unable to form a constant, predictable sense of self and the world; unlike the healthy child, the borderline is unable to establish a healthy object constancy -- a reliable, comforting, internalized image of her world -- that she can use to soothe herself in time of stress. Instead, she needs the presence of others to reassure and comfort her."
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The passage also has an anecdote about a woman named Arleen (who has BPD) where she is quoted to say, "I feel I really couldn't be myself without another person to reflect on."
Also: this is the updated version of I Hate You, by the same authors, taking on feedback and criticism of the earlier book, and rewritten as Sometimes I Act Crazy.
Honestly, I would reaaally advise you to get into therapy. BPD is difficult enough to manage even with DBT, so I don't know how well you can cope trying to work on it on your own.
If you're really sure that's what you want to do though:
Get your hands on as many books about BPD as you can. Personally, Sometimes I Act Crazy was a pretty good read. Get Loving Someone With BPD for your boyfriend. Get a DBT workbook. This is the one I'm currently using. r/dbtselfhelp for more resources.
Screaming and yelling at your BF won't solve any of your problems; it's just a coping mechanism for you to unload all the horrible emotions you're experiencing. Recognize that. When you feel it coming on, tell yourself, "This is just a coping mechanism. I can be strong enough not to use it. I can manage this in other ways."
If you feel yourself getting angry and you want to act out on it, imagine putting yourself on pause. Don't react, as much as you want to. Just breathe, focusing on every breath moving in and out of you. When you feel calmer, then begin to ask yourself why you're angry. Anger is a secondary emotion; there's usually an underlying emotion beneath it that's the real culprit.
For example, you were mad at your BF about the veggie mix-up because of emotions such as fear that eating his lunch would make you fat and ruin your progress. I don't know about the full story, but maybe you were mad about the haircut because you felt scared and sad that he hadn't told you about it. Maybe this is just part of a long string of events where you consistently felt like your BF was leaving you out. Maybe the haircut caused him to be late in meeting you and you felt sad that he hadn't given thought to your feelings.
Dig deep and figure out what the real reason is. Then you can begin finding a solution that targets the real reasons. Explain the reasons to your BF: "I feel angry with you because I'm putting in a lot of effort to try and lose weight. Now that you've taken the wrong container, it's making me afraid that this lunch will destroy all my progress." or "This might not be the actual truth, but the fact that you didn't tell me about your haircut made me feel like you don't even care about me."
You won't be able to stop yourself every single time, especially in the beginning. But try your hardest to minimize the casualties. Control it as much as possible, and you'll see yourself starting to improve. If you slip up, apologize.