If he shows up and his phone rings off the hook, and he keeps looking at it and then shutting it off, then it may be because the ladies are calling him 24/7. If he's texting as soon as you step out of the room and abruptly puts away his phone when you show up, then you're not the only girl in his life. And if he never leaves his phone unattended, not even for a second, then it may be because he doesn't want you to see all of the sweet texts from his other side pieces. Let's say you're his Facebook friend, and you better be. Check out his profile and see if there are tons of girls messaging him, if he's flirting all over the Internet, and if there are dozens of photos with him looking booze addled and surrounded by scantily-clad women. If that's the case, then you know where he goes when he falls off the radar for five days; and it's not just because he's having a crazy week at work. If his Facebook seems completely unmanned or if it looks like he rarely uses it, and yet, you know he watches your every Facebook move, that's definitely not a good sign. Have other women come up to you and told you to stay away from him? Have your friends told you that he's a player, and that he'll never be your boyfriend? Unless you think you can "tame" or "change" him, (and you can't) then these are bright red flags that say it's time to call it quits pronto. Don't think that you're different, or that these women don't know what they're talking about. If you've heard it from multiple people, then chances are, they're right. Has it been six months and you still haven't met his friends, talked about the upcoming months in your lives, gone shopping together, hung out during the day, or done any of the things that normal people do? It's okay if it takes a long time for him to say "I love you," but if he has rarely even said, "I really like you," and it's been a while, then things may not be moving forward because he only sees you as his plaything. Wake up! If you're even contemplating this might be a possibility, you've got a gut...

TL;DR in Vietnamese:
Điện thoại của anh ấy có luôn rung chuông mỗi khi ở cạnh bạn? Kiểm tra tất cả các cô gái trên Facebook của anh ấy. Bạn có từng bị cảnh báo hay không? Có phải mối quan hệ của bạn không tiến triển gì? Hành động theo cảm tính của mình.