@DLC90,
DLC90 wrote:One part of me says go, the other part of me says stay.
Listen to the part that says "stay". I won't comment about your marriage, I don't need to because this bird won't fly just on the immigration aspect. The UK Border Agency will bounce your ass back on the next plane. You won't even get into the country.
To enter the UK, you need a visa. Citizens of certain countries including the USA, can arrive at the airport, fill out and sign a "boarding card" in which they declare the purpose of their visit, and present their passport to the UK Border Agency agent, who has police powers. By doing this and stating that the purpose of their visit is a vacation, they are applying for a vacation visa, which can be granted or denied. If it is granted, you get a visa stamp in your passport with an expiry date. If it is refused, you go back on the next plane whether you want to or not.
Americans cannot just "move to England". Unless you have a costly and very difficult to get visa, you can only visit for a vacation, maximum duration 6 months. They can question you about this, ask to see return tickets, evidence of ties to the USA, and if in doubt go through your baggage, phone, etc.
If the immigration police officer thinks you are lying about your real reason for coming, they can refuse you entry, place you in a detention area at the airport, remove you from the country, and ban you from the UK for up to 10 years for using deception to try to enter the country.
They do this to thousands of people every year, and a lot of them are Americans who are meeting someone they hooked up with on the net. They are very very good, they know the signs and can spot them when they are way back in the line waiting to show their passports.
Unfortunately there isn't a "trying out a web relationship for real to see if it works" visa. If you managed to get through and hooked up with the girl, you wouldn't be able to work or get healthcare or welfare benefits because you would be an illegal immigrant. and in the unlikely event that the girl thing worked out, you would have to leave when your tourist visa expired or risk jail, deportation, and potentially a lifetime ban for being in the country illegally (since you got your visa at the border by deception) and overstaying.