Would I be considered an over-stayer?

I'm a US citizen, engaged to marry my UK boyfriend this autumn. We've been together as a couple for four years (he's spent time in the US, I've spent time in the UK) but have not previous lived together. We're planning to marry in the US in September. Here's my question (with apologies for the fact that it's a long-winded one):

I've spend a lot of time in the UK over the last 15 years -- anywhere from 3 to six months each year. I always came into the UK on a visitors visa and I never over-stayed the visa. I never worked in the UK, I always supported myself on income earned in the US, and I've maintained a home in the US the entire time.

Last year, for the first time, I spent more than six months in the UK. I spent six months and then, right before the visitors visa expired, I spent a weekend in France, returned the UK, and got another six month visitors visa stamp. I spent four months in the UK on that stamp, and then returned to my home in the US (along with my boyfriend), where we stayed for six weeks.

We recently returned to the UK. I naively thought that I could come back into the country for the summer without any difficulty. I thought that as long as I had a home in the U.S., didn't work here, had enough funds from the U.S. to support myself, and didn't overstay the visa dates, it was still okay for me to be here on a visitors visa stamp. Boy, was I wrong.

The immigration officer explained that it wasn't okay at all -- that I'd been here too often and it looked like I was trying to settle here without getting the proper permission. After a long discussion, she did in the end let me enter the country and she gave me another six month's visitor's stamp, but she also told me sternly that I had to leave by the exit date and then either spend at least a year back home in the US, to prove I lived there, or -- if I wanted to return -- apply for a residency visa of some sort, such as a spouse or fiance visa.

So, okay, we've decided to get married. We'd been planning to anyway, this simply made us stop procrastinating. We've learned that we can't do it in the UK while I'm on a visitors visa, so we're going back to the US in September, where we'll tie the knot and to apply for a UK spouse visa. Then my boyfriend will come directly back to the UK while I wait for the visa in the US.

This is a long-winded way of getting around to my 3 questions, but I wanted to lay out all the potentially relevant facts first. My questions are:

1. Will I be considered an over-stayer, due to the amount of time I've spent here (either recently, or over the years), even though I never technically overstayed any of the six month stamp dates?

2. Have I landed myself in serious trouble over this, and do I now have some kind of immigration file? (During this last entry into the country, I was soundly scolded and the Immigration official wrote something down on my landing card in pencil ... but I was nonetheless given leave to enter. In addition to usual visitor's stamp, dated in June, there's an addition stamp that says: HBR 08 402 - Leave to enter for six months. No work or recourse to public funds. )

3. Is all this likely to raise a big red flag when we submit our application for a spouse visa -- and is there anything that I can do now that would help?

I'd be very grateful for advice.

1. Although visitors are not normally expected to spend more than six of twelve months in the UK, I don't think that you will be considered an overstayer when paragraph 42 is met.

2. Probably not serious trouble as you were given leave to enter.

3. 26.17 Refusal where the applicant has previously breached the UK's immigration laws.

Thank you for your help.