Boyfriend claiming ex girlfriend pulled a knife on him

I made a post earlier about my boyfriend. We are 19. He lives with his parents. He has been distant from me and this was the letter he put in his dresser

I asked him about it and he immediately got defensive about me going through his stuff. I told him I want to know about this and he said his ex girlfriend hasn't left him alone in 2 years. It's the girl he claims he dated when he was 17 and she was supposedly 23. Buy he's saying she's obsessed with him and will randomly call him from different numbers. I have seen her do that but I've never seen her show up to his house. He is saying she did and when he went to ask her to leave that she struck him first and pulled a knife on him. Does this sound fishy? If she's an ex than why was she charged with DV? Also he's insinuating that she's so crazy she just pulled a knife on him for nothing? What normal girl does that? They will have court over this it seems so I guess the truth will come out there