If my BF left me while I am pregnant, I won't take him back.

From your post, your BF is a trash. How could any decent person treat the mother of his child like this? ("他就消失了，期间只给我发了2封邮件，第一封建议我去流产，当时孩子已经将近22周，第二封告诉我我不是个好人，时间会证明一切。")

I think adoption is a valid choice for you. You can select adopting parents, i.e., find a good family for the baby. I do understand that no mother wants to give her own baby away. However, the reason should never be that "wish the baby's father to come back to me one day". Being a single mother is tough; but very doable, especially in the States.

No matter what your choice is, good luck!