I am very glad you are taking your medicines and doing what you can to understand yourself and your fiance. You are wise not to let this situation derail you from your own treatment.
You’ve done a lot of work to try to understand yourself and your guy. Your conclusions regarding diagnoses may or may not be correct. You don’t have the training to interpret symptoms. But your own good sense tells you that both of you have many issues that deserve attention and that need to be dealt with if you two are to have a happy life together.
What you don’t mention is what work your boyfriend is doing. From your letter, it sounds like you are the one who made the effort to draw boundaries around your fiance’s involvement with his brother’s girlfriend. You are the one doing the research. You are the one who wrote to us here at Psych Central. This concerns me. When one person does all the work of a couple, it is like one hand clapping. It doesn’t result in a sound.
Yes, you do need to sort out your issues — an important one being why you stay with someone this emotionally unstable, another being why you are aggressive toward someone you love. But for the two of you to be happy together, he has to do his share of the work as well. You both need counseling. You also need couple counseling. If you love each other, you will each (both of you) do the work you need to do to learn how to trust and be worthy of trust; how to love and be loved without hurting each other.
I wish you well.