From you words "我明白，我對愛情是不專一，但我對每個我愛的人也是認真的，雖然這是做錯的事情！"
I strongly believe you are a playboy actually. Every playboy after they hurted a girl's heart, they will say this to the girl and your friends. What was your intention? I think everybody should understand this. But I can say you are not entirely a true playboy. Otherwise, you won't care what you did and setup a topic for us to discuss.  

Man,it seems that you accept a girl so easily. I think it is now you come to a point that you should decide whether you can promise yourself you can only have one girl in your brain in the future or not. If the answer is no, then you shouldn't marry again. Stay in the playground, have many girlfriends at one time.

This is the experience that I saw from my friends. Hope it can help you to know yourself better.

Dear fuXkallday
           Thanks for your advise. Obviously, the approach you are using is quite self-centered. Girls are not stupid, perhaps the girls who approaching you were stupid, but at the end of the day, they will figure out you have gf. Perhaps, she will take you from your current gf. Do you think she will trust you and treat you serviously in the future? In my opinion, how come girls nowadays become tricky and don't treat love affairs seriously, is becasue there are so many mens using the approach you suggested. From what you have written here, I guess you are having simular attitude to Kenny1234.  In realiaty, it is hard to distinguish what is correct and what is wrong. Beside, self-centered and self-fish are associated each other.