I am from the UK and have been dating an american guy for a couple of years and We now want to take this further and hope to get married eventually, I am planning on taking a career break (just to cover my options) and want to go on an extnded visit to the states, I have looked into this and it appears that my best option is via a B12 visa. I have visited him on several occasions under the visa waiver programme but these stays have been for a maximum of 3 weeks and I believe you can only stay a maximum of 90days. Please can you advise if this is the best way and what criteria you need to furfil to get one. I can take some cash with me but mainly my Bf and his family will be supporting me, if this is not acceptable how much currency would I need for the maximum 6 month stay.

This would be a difficult visa for issuance.

The B-2 visitor visa is typically not issued as the U.K. is a visa waiver (ESTA required) country. To get the B-2 visa, you need to prove to the CONOFF you do not intend to immigrate to the US and have sufficient funds to pay for your visit so you will not work unlawfully. But, you have a US boyfriend, no employment to return to, no significant savings and are planning for support from your BF and his family; it is very unlikely for the B-2 to be issued.

It would be much easier to enter as a visitor on the VWP. Good luck, and post again if you have other questions.