What happens if i share my apple id with someone?

So i have my apple id and my boyfriend wants to share it & use his credit card for it (he wants to use it for his iPod to get music) he has the iPod nano 5th generation. So i use my apple id for my iPhone and I'm wondering if he uses it as well, will that mess anything up? Besides music, like will he be getting my iMessages or emails or pics or apps on his iPod? I'm not even sure if his iPod has those features i know the iPod touch does though which is why I'm curious and I'm just wondering.

You can manage that in Apple ID settings including photo stream and iCloud