I have a new puppy which turned out to be something else?

I adopted my new puppy about 8 months ago. He is 9 months now. He is fun, crazy, SUPER cute and it was supposed to be a boxer mix. He had a tragic birth, his mother died at birth and he was left in a dumpster to die when he was born. Thankfully he was rescued and survived. As you can imagine when I heard his story, I had to adopt him. The issue I am having is that as he grows he not looking like a boxer in any aspect of his features. I did research and it seems more likely to be a full blown Pit-bull. I have two other dogs, Lhasa Apsos, and he generally gets along with them except on some occasions he has turned on them, luckily I have been there to stop the fight. He is growing immensely each day. My question is...Is it safe for me to keep him (I AM UTTERLY IN LOVE WITH HIM)? Anyone with experience with Pit-bulls who is not Cesar from the Dog Whisperer...LOL....please give me some feed back as to what you all think I should consider doing.