Why Does My Kitten Keep Hissing At Ne?

I have a kitten. I got her when she was 2months old. She is very sweet and loving, but not affectionate (she can be handled, but she doesn’t like it).

When i first got her, I noticed that she seemed scared of my boyfriend’s hand or arm. So I took out the leash to walk with her around the block (because this usually calms her down). Well guess what? It still does! We went back inside and took some pictures where I petted him on his arm so he wouldn’t notice… But every time he gets near me now she goes nuts! She growls at him or runs away from him so fast! What should we do about it?! And how long will it last for? :\

We are trying to teach them socialization too because they are both kittens, but nothing really seems to work 🙁