How do you stop receiving Facebook notifications on certain cell phones?

[Chase]

Ok, so almost every time I go to my best friends house I use his smart phone to check my Facebook, and now for some reason my notifications get sent to his phone, even when I'm not logged into facebook on his phone, I went to mobile settings on my Facebook and his number isn't on their, so why are my notifications getting sent to his phone? and how do I turn it off? Cause now everytime I go over to his house, he gives me a hard time and knows who I've been talking to on Facebook. Any help would be greatly appreciated, thank you all.
(SARAH), It's not that he's purposely looking at my messages, it's when someone on Facebook sends me a message, his phone goes off and it pops up on the top of his screen and shows the message, but I just now went and changed my password and it asked if I wanted to be logged off of other devices, meaning other computers and phones, and I clicked yes, so hopefully that worked, but if now I'll try your idea and have him log onto his account next time I go over there. Thank you