100% SCAM - there is NO such thing as a BTA. That is a term invented by online romance scammers
This BTA scam is so common even the US Embassy in Nigeria has a warning about it on their website
"Beware of anyone who requests funds for a BTA, or Basic Travel Allowance, as a requirement to depart another country for the United States. There is no such thing as a BTA. In other cases, your Internet friend will claim to need a travel allowance, or travel money, to be able to travel to the United States. Again, there is no such requirement under U.S. law."
All anyone needs to leave Nigeria is a plane ticket and passport. There is NO new law - I work for a company with our African regional office in Nigeria and can guarantee with 100000% certainty there is no such thing as we just had staff fly out of Nigeria last week
Also, he is full of crap that you can't use a credit card in Nigeria. Nigeria is not some backwards country - they even have skyscrapers there. This is Lagos Nigeria http://cheapflights2africa.com/images/modules/countries_management/lagosflights.jpg -- it's a modern city that has a huge banking and finance capital and definitely accepts credit cards.
It's the fastest growing economy in Africa and one of the fastest in the world. You can use credit cards at any big hotel, expensive restaurant, travel agency, airline office, department store, etc -- not to mention you can get a cash advance on your credit card at any major bank like Ecobank, Zenith Bank, etc or use it at any ATM
I can guarantee you've never actually met this boyfriend - because he does not exist. You have been conned by some 19 year old "yahoo-yahoo boy" in an internet cafe who stole pictures of some handsome man off a social networking or amateur modeling site, set up a fake profile, and is using it to scam women out of hundreds if not thousands of dollars. I can also guarantee you've never talked to him on video or you'd know he's not the man in the pictures. Pretty much every internet cafe in Nigeria has webcams and Skype so he is full of crap again if he claims he can't do a video call
Want to prove it's a scam - write back to tell him that you just spoke to the US Embassy in Nigeria who confirmed there is NO such thing as a BTA and that if he can't use his credit card he can go to the Embassy and they'll give him an advance that he has to pay upon his return. Say that the embassy said if anyone at the airport asks him for a BTA he needs to immediately call the Embassy and they will have a representative meeting him in less than 30 minutes to ensure he does not pay anything and escorts him onto the plane.