what if i love him but he doesnt feel the same?

i love this guy so much.... i met him when we where younger... but lost contact then we met by facebook and we started talking again then he ask me out and i said yes but then the very next day his nephew says that he was talking to another girl... i asked him he told me that she was flirting with him... and i asked him what did he do? he told me all he did was sit there and watched and type... that broke my heart.. days later i asked him if he loves me and he said " danielle i love you with all my heart" i tole him i feel the same way but i am not sure if he is telling the truth becuz he tiold my best cousin that he liked that girl that was flirting with him and then he tells me that he does like her at all becuz she went out with his nephew 3 times and cheat..... what am i suppose to do?