Gawd... I had all these 'flyer miles' saved up from YEARS of work that had involved a lot of travel... and I used them all in like... a year and a half!!! Or just over that?
We made a rule: No more than 6 weeks apart. And we totally stuck to it. On the last day of all of our visits, be booked the travel, for when and where we were going to see each other again.
In hindsight, I must say, we were so very lucky to be able to do that!
So, every six weeks, either one of us, or both of us, got on a flight.
We sometimes both flew to a third country to meet up, or he came to NYC, or I came to London. Some of the visits were as short as 4 nights, and one was as long as 3 months.
I never had an issue flying into Heathrow. And he never had an issue flying into any of the airports in and around NYC.
I think every case is different tho. It seems to be 'the luck of the draw' in many ways. I know some people who have had some problems.
I always had everything ready: Proof that I had a job, proof that I was enrolled in a grad school programme, proof of funds... The usual. But no one really seemed to care that much.
But, my now hubby, then boyfriend, never had 'proof' of anything on him. And, so, I often worried! He owns a business and a house in the UK, and I always asked him to carry some sort of proof, just in case, but he brushed me off, and never bothered. And, it was never an issue.
I think the only time I was really asked about anything specific was when I came over for a month, and then flew back to NYC for 4 days, for an exam, and then returned for another month - But, I just told them why I had done that. I had all the proof ready, but it was not looked at at all. I was just 'asked' why I went back for only 4 days.
They always asked me why I was entering the UK, and I just said, "I am visiting loved ones."
They seemed fine with that response. They never asked for any details.
I basically spent most of 2010, strapped to a seat, on international flights.