In my first reply to you I didn’t pay attention to the fact that your boyfriend had sex with another woman after the two of you broke up, so he didn’t cheat on you. The question in my mind: is it right for him, now that he is back with you, to be friends with the woman he had sex with?
Assuming that (1) you are and have been faithful to him throughout the exclusive part of the relationship, (2) that you are not friends with men you had sex with in the past, particularly in the recent past, (3) that you are very hurt and very distressed about his friendship and that he was made aware of it, then I’d say that it is wrong for him to be friends with her, primarily because it hurts and distresses you.
“He says he will not stop talking to her because they are friends but he only love me“- doesn’t he love you enough to not hurt and distress you unnecessarily?
“What should I do?“- do something (better than doing nothing and suffering silently day after day, night after night): either ask him that the three of you meet and talk about the situation, and/ or let him know that it is his friendship with her or his relationship with you and then follow through.
Your screen name is help with love: I am thinking that the help you need is not with his love but with his selfishness perhaps. Do you think so?