If someone did this what would you do?

I no this boy he told one girl he loved her with all his heart and she was is ex-girlfriend and they were best friends after the brake up. And he says it all the time to her. Thin he goes in tells another girl hes in love with her and both of the girls used to be to be his girlfriends and both girls broke up with him before win they were together I wasn't really shear why he did that. What do you think the first girl should do I found out about this yesterday I don't no what to say or do. Help help!!!!!!!