Know how you feel. don't have a T or anything so really cannot get a handle on the precise nature of things, whether living in a 24/7 dissociative trance expressed creatively at times or whether living with bona fide DID. But having recently become aware of its own deterioration, this one can sympathize with the idea of having a "bad" (dangerous, hurtful) alter. That must feel very scary to you, to be out of control like that and on top of it worried that others might see that as YOU doing "bad" things on purpose.

Your boyfriend sounds truly amazing indeed, to be willing to cope with all that. Certainly he loves you a lot! Take comfort in that. If you have a T maybe you can enlist him/her to help you work on making contracts with that 'part' for things s/he can do to de-escalate and/or seek help when 'forefront' and feeling hostile or unsafe?

Stay safe.