Do it yourself, but use us. Promise you won't get rejected.
You can either:
1. Marry somewhere other than the UK, return to the US and apply for a spousal visa
2. Return to the US, apply for a fiancé visa, return to the UK, marry, then change to a spouse visa.
A spouse visa allows you to work, study, volunteer, and use the NHS from Day 1 after you land in the UK.
On a fiancé visa you cannot work, study, volunteer, or use the NHS until you switch to the spouse visa. You also have the cost of a second visa to apply for.
The choice is yours!
Does your fiancé make enough money to sponsor you (more than £18,600/year)?