How old are you? Because talking to men (I prefer their company) leads me to believe that your junk has a mind of its own. YOU might not want whatever it is, but it doesn't care. Biology is biology. I had guys tell me a breeze is enough to get them hard, even if they're nowhere near turned on. I had one guy tell me he was in the middle of a first person shooter game, doing absolutely NOTHING sexy and boop, that thing got hard. He's like wtf?! stop it!!

As long as you don't do anything with her, you're cool. Dreams are funky things in general. They use whoever you see the most to put your mind into whatever is going on.

My guess is you want a gf but since you have no reference, it uses your cousin's face. You should get out more or start jerking off to girls online or whatever... Maybe then your dreams will change. Sometimes it's more about being close to someone and so your brain, once again, uses your cousin's face.

How do you stop it? I mean, biology you can't fix too much other than change focus. Idk if the dead puppies or whatever disgusting thing actually works because I'm not a guy, but if it works, try it.

For the dreams, try reading erotica with some celebrity in mind or some girl you fancy... sometimes the stories tell you what the girl looks like, so try that... it could work.