How can you tell if a boy is in love with you?

just wondering. There is this boy who is 16 and im 19 and his mom says he loves me. But it bothers me to think he is messin around with other girls. Do you think he will?? I dunno. his mom says he hasnt dated anyone since me. So im just wondering. Ha. thanks (: (but he is a "boy" still so i guess its hard to tell.)