밖에 없다 means there's nothing/nobody else except something or someone. It always combines with a noun before itself. -ㄹ 수 없다 means there's no way to do something, so 공부할 수 밖에 없다 use two negatives, i.e. you have to study. When translated into English, it comes out as 'You can't help but study'. The original form is -ㄹ 수 밖에 없다. (수 means a way/method, ability etc) 너/나 밖에 없는데. There's nobody but you/I. (cell phone conversation) A : 둘 다 지금 내가 있는 데로 와. You two now come to where I am. B : 여기 나 밖에 없는데? But I'm alone here. (implies 어떡할까? or 나만 거기로 갈까? etc) A : 뭐? XX(their friend's name)이 어디 갔어? 둘이 같이 있었잖아.

"only you"

"너밖에 없는데" means "Nothing except you"