Your best friend's sexuality is her own business. If she might have a crush on you, however, you can help defuse this and save the friendship. If that's your goal, reframe your thinking. You don't need your friend to confess; you just need to return to an uncomplicated friendship. Never tell someone else you think your friend is a lesbian. No matter how progressive your school or town is, someone could bully or harass your friend because of that rumor (even if it is not true). You do not have to be 100% certain before you do something. You will probably continue to suspect something or second-guess your friend until you clear the air. However, if you are hesitating or doubting yourself, you can check for the following signs of a possible attraction:  Physical touch is common in female friendships, but only to a point. If your friend holds your hand on the street, gives you massages, or hugs you for an unusually long time, she might have a crush on you. (The boundaries are different in each culture, so these examples don't apply everywhere.) She contacts you constantly, and gets upset if you take too long to respond. She gets upset if you spend time with other friends instead of her. There are ways to defuse the situation without prying into your friend's personal life. During a private conversation, make it clear that you are not interested without putting your friend on the spot. Here are a few hints you could drop (but only use them if they're true):  "I really want to keep you as a best friend. Can we stay that way?" "I want to find a guy to date." "I would like us to spend more time with the rest of our friends, instead of one-on-one. Are you all right with that?" If you have cuddled, kissed, or done anything else with your best friend that could lead her on, stop and think about why you did it. If you are definitely not interested in dating your friend, this behavior can lead to heartache. Set new boundaries for your relationship, even if she tries to argue with you. Say "I think we should stop...

TL;DR in Vietnamese:
Tôn trọng quyền riêng tư của người đó. Tìm kiếm dấu hiệu. Từ chối một cách nhẹ nhàng. Làm rõ dấu hiệu gây hiểu nhầm. Trực tiếp giải quyết vấn đề với cô ấy. Xa nhau trong một khoảng thời gian. Cảm thông.