I am clearly pretty inept at this kind of thing, seeing as I was refused entry to the UK back in the fall. The experience did make me realize, though, how naive I was about international travel. Someone else may be able to give you more solid, reliable advice, but I would say that if you do make the trip you should have more than proof of a return ticket with you. When my husband (UK resident) came to visit me in the US at Christmas, we were advised by US immigration to have proof of his return ticket, a statement from his employer on company letterhead saying when he was expected back at work, the lease contract for his flat in the UK, his registration card with his country's embassy in the UK, proof of bank accounts in the UK-- anything that would persuade the IO that he had no intention of staying past his return ticket date. Again, that was for US immigration, but I would imagine that those same kinds of documents might work for the UK too. Also, is there anything that your boyfriend can provide to show that he's currently residing in the US as well?