If a boy emotionally separates himself from a girl then after a period of time starts talking to her again can he get her to fancy him as a boyfriend?

Yes , ofcourse he can ! Although , the girl is probably confused of why the boy cut himself of from her in the first place and probably scared of getting attached incase it happens again . Try explaining to her why you did it , and reasure her that it wont happen again .

Good Luck !