agnes, your best bet is to post this question on britishexpats forum. It's a very friendly forum that is full of people who want to help you as much as they can. Some of the posters there are very knowledgeable (myself excluded

). The forum link is
http://britishexpats.com/forum/us-immigration-citizenship-visas-34/.
As for your question, you'll most likely receive the same answer on the british expat forums as I'll give you: get married. It really is the most simplest. Your partner will likely get an L1A or L1B visa (inter-company transferee), and if you get married, you will be eligible for an L2 spousal dependent visa.
This will allow you to work for anyone (once you get your Employment Authorization Document). If you don't get married, you could be eligible for a B2 cohabitation visa, but
you cannot work with it; not even remotely for a UK company from the USA. The H1B visa is a potential route for you, but you have to have a US employer to sponsor you for the visa, which costs thousands of dollars. Most employers only qualify for the capped H1B visas, which means that the soonest that they can apply is April 2017, for a visa that won't be granted until October 2017, if successful. In addition to this, the employer only has a 1/5 in chance of getting a visa in 2017, given how oversubscribed it is. However, there are cap-exempt H1B visas, which certain institutions can qualify for (not-for-profit higher education institutions, not for profit research organization or a governmental research organization, certain for-profit (e.g. consulting/contracting) firms, etc). Investment visa (EB-5) is a possibility, but you have to have hundreds of thousands of dollars of spare money that you can afford to lose, and not many people have that.
The visa waiver program allows you to travel to the USA for 90 days without having to get a visa, and you'll be admitted as a tourist (leisure trip) (B2) or business (meetings with clients, etc) (B1). Technically, you can apply for a "change of status" from B1/B2 to H1B, but the chances of finding an employer to sponsor you and having everything wrapped up and done in 90 days are quite low. If you do have to leave, you *shouldn't* return to the UK and come back straight away, as the border agents won't take too kindly to that. The general rule of thumb is "stay outside of the USA for longer than you are in the USA". If you visit the USA for 90 days, you should return to the UK for at least 91 days, before returning, etc.