How can I get my friend to stop talking/ liking this girl that I like as well without ruining our friendship?

Yikes. Try talking to your friend because it wouldnt really be fair for either one of you to date the girl in front of the other. So either way one of you guys would be mad and the friendship would most likely get ruined.

Tell your friend that you like that girl and it's making you upset.

you cant ---- I suggest one of you ask her out and see who she likes

You don't. You learn that you can't control everybody and everything, and that the whole world doesn't revolve around you and what you want.

you can't just stop something like that. But, if you really don't want them to with her, tell your friend how you like this girl too. That may make it awkward for them to date her, but at the same time that also goes for you