Should i travel across country Alone?

i want to travel, about 3 years ago i met a guy from south africa (victoria), he came here to the states on a workers visa for 6 months we hung out a lot then, when it was time for him to return home he invited me to visit we've kept in contact off an on through e-mails an long distance phone calls, now hes being very adamant about me visiting , oh yeah he also keeps saying were going to get married when i get there, not even joking (i dont think). when i ask him to return to the states he says he cannot without telling me an exact reason, i would love to see the world an other countrys but theres always that story of the americn that never returns (you know) . what should i do check out his backgroud online (can i), trust his word, ignor him? even though i'v known him for 4 or 5 years via e-mails an phone i still dont know if should trust him, the 6 months he was here he was very sweet an we pretty much connected, am i over reacting & over yzing. should i visit this friend.