@basefan Dogs can definitely pick up on nervousness and mirror those emotions. More likely is that he's fresh from the shelter and his traumatic past, and reacting in extreme fear at anything he doesn't understand. It doesn't make it okay but that's probably what is causing him to bite, moreso than his read of your behaviour.
That said, I don't know this dog, and neither does your boyfriend. He doesn't know all his triggers and his traumas. He can't know with any kind of certainty that it was your behaviour that triggered the dog to bite. It sounds like he's using that as an excuse to placate you, because he knows you're unfamiliar with dogs and won't know otherwise.
If your bf had an ounce of common sense and responsibility, he would eliminate the possibility of the dog harming anyone during this unpredictable, volatile phase. And he would do so with urgency and care,
especially now that he knows the dog is reactive enough to bite.
Furthermore, he would have immediately hired a trainer for this dog upon adopting it, regardless as to whether or not he bit you. A cane corso pitbull mix is an extremely powerful, strong-willed, high-needs dog with a shit ton of drive. That is an extremely challenging breed combo even for an expert handler. A dog like that has the potential to be
lethally dangerous if mishandled. And without knowing his history, your bf has absolutely no idea as to the level of risk the dog currently presents. ANY PERSON adopting this dog, irrespective of any existing knowledge and experience, should have had it
immediately assessed by an experienced trainer or behaviourist. It's absolutely critical to inform and prepare yourself as the handler to be able to safely manage any dog with an unknown history,
especially when it's a power breed. I'm upset (but sadly not surprised) that the shelter didn't insist on this as a prerequisite to adoption.
Beyond all that, most concerning is your boyfriend's attitude towards
you. It's not "his" dog, you live together and the dog was brought into your
shared home. Your bf completely disrespected your agency and disregarded your needs and your safety. If you're not comfortable around a dog like this, you have every right to not be forced to live with one. After the first instance of aggression, you had every right to demand that the dog be removed from your home, and/or safely confined, and/or muzzled, until such a time that you have full confidence he won't cause any further harm. And frankly,
your bf should have insisted on it himself, and taken the initiative to protect you and ensure your safety. The fact that he not only neglected to do that but actually
downplayed your concerns and made you question your own feelings and opinions really says a lot about his priorities and how important he considers you in his life. Not to mention, dismissing this violent reactivity puts Oscar's life in jeopardy as well. Clearly, this is his world and you and this dog are just living in it. If it were me, I'd be done. I know that's not the advice you came here for, but it's by far the biggest issue with this situation imo.
And if this is the kind of selfish, irresponsible person he is, he's honestly unfit to be the owner of
any dog, let alone one with needs and capabilities like Oscar's.
Edit to add: OP, you're in imminent danger as long as you're around this dog. I see your edit that your bf will find a trainer. Until then, the dog needs to be crated, muzzled, and/or kept in a separate room. It will suck for the dog for a little while, but you really shouldn't mess around with this. That dog has the power to literally kill you and/or permanently disfigure you, please take it seriously.