Is he just messing with me?

ok i met this guy he is from another state. i have a bf and he has a gf. i really like him and he is talking about wanting to be with me. how do i know if he is sereous and not just messing with me? i have never met him in person we just talk on the phone. he is talking about coming to meet me and i told him he couldnt if he still had a gf because i would break up with my bf before doing that because its not fair to him. he tells me he would break up with her in a heart beat for me. how can i tell if he is sereous or not? would a guy call some girl in another state using all his cell min when he has never met her and just be messing with her?