Booking Flights to UK

Hi there, so just waiting to hear back to see if I will be clear with my Fiance Visa, but now I'm anxious to look for flights.

I figure it's ok to at least look and plan but I probably shouldn't book until I know for sure right?

But here's the question....My fiance is in No Ireland. Does this mean i have to book my flight from US to Belfast? Or am I ok to go to London, then Belfast? I know I definitely shouldn't go through Dublin because they give you a Ireland stamp rather than a Uk stamp, but does it matter if it's London?

So long as you don't fly directly into the Republic of Ireland, you are good to go.  London, Belfast, Manchester, etc., doesn't matter.  Even anywhere in Europe and then either train, ferry, or flight into the U.K. is fine.  It's literally just the ROI for that initial entry (fair game after that).

And yes, look but don't buy.