Once you've made your decision, stick to it. That doesn't mean you have to tell the guy, "Hey, I chose you over Guy A!" That won't make the guy feel very special. The commitment is something you make through your actions and your heart. Work on building a healthy, stable relationship with the guy you've chosen -- and only the guy you've chosen.  Get ready to start dating and hanging out with only the guy you've chosen. Enjoy the benefits of being with one person without wondering what another guy is up to. If you feel empty or incomplete without the other guy, then it may either mean that you made the wrong decision or that you never liked the first guy that much in the first place -- you only liked the chase. Be friendly to the other guy but don't go out of your way to hang out with him or do stuff alone together. If you're overly friendly with him, he might think that he still has a chance. Plus, it might get the guy you chose unnecessarily jealous. Know that choosing between two guys will affect your relationship with both of them. This is the double-edged sword of relationships: chances are good that you're going to break the other guy's heart and miss out on a relationship with him. If the guy you don't choose doesn't know about the first guy, you don't have to make it a big deal or give him the real reason why you're ending your "relationship." Though you should be happy once you've made your decision, know that the seas may still be a bit rocky.  Know that you may turn guys against each other. What if both guys are best friends? What do you do then? If you choose one and the other likes you, they'll probably stop being best friends. If you want to avoid this situation altogether, date someone else instead. Be prepared to lose the guy that you didn't choose. He may not want to be "just friends" after you hung out romantically or flirted with each other. But that may be for the best. Life is yours to live, and you deserve to live it the way you want -- while trying to hurt others as little as possible....

How would you rephrase that briefly using Vietnamese?
Hãy chân thành với người mà bạn đã chọn. Luôn sẵn sàng đối mặt với hậu quả. Hãy chấp nhận quyết định của mình.