Welcome to the forum
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Not sure if you are aware, but if you wanted to skip the fiance visa step and just come back on a spousal visa right away, you could marry easily in the US first, before applying for any more UK visas.
Fiance visa- valid 6 months
- must marry in the UK within the 6 months and then switch to FLR(M)
- can be anywhere from 35 days to 77 days before you can marry due to residency requirements and giving notice periods
- no work or study allowed until you have FLR(M)
- no NHS access until you have FLR(M)
- must have private travel/health insurance
- fiance visa costs: £956
- FLR(M) visa costs: £649 (will rise in April 2016 though) plus £500 NHS levy
Total visa cost in the first 3 years: £2,105
Spousal visa- you both fly to the US and get married (no waiting period, other than maybe 24-48 hours), then apply for the spousal visa
- spousal visa is valid 33 months (issued as a 30-day vignette allowing you to enter the UK, then you pick up a BRP card within 10 days of arriving in the UK)
- visa costs £956 plus £600 NHS levy
- allows immediate work, study and NHS access
Total visa cost in the first 2.5 years: £1,556, but you also need to pay the extra flights to and from the US to marry