How to say in Korean: Are you alone?
I heard something like 혼자서?
What is the different between 혼자서 and 혼자예요, and what is the different between the ending 서 and 요?
Thank you :)

Question

How to say in Korean: Are you alone?
I heard something like 혼자서?    
What is the different between   혼자서  and  혼자예요,   and what is the different between the ending 서 and 요?
Thank you :)

Answer

I guess you heard 혼자세요?

Are you alone? 
means  "혼자세요?" or "혼자예요?" in Korean.

"혼자세요?" is honorific form of "혼자예요?".

All verbs and adjectives can be converted into an honorific form by adding the infix -시- or -으시- after the stem and before the ending.

혼자예요 is composed of 혼자이(다) + 어요.
혼자세요 is composed of 혼자이(다)+ 시 + 어요.

Answer

외로워요? or 외롭습니까. From my Korean national friend Boona.