It sounds as if you have been staying as a visitor for a few months, hopping to CZ or the US for work and coming back to live with your girlfriend. The 6 months out of 12 applies to ALL visitors, except visiting academics. If you are not in the UK under a different settlement path, you are here as a visitor.
If you are entering as a business visitor or a prospective entrepreneur, those require a specific type of visitor visa.
I spoke at length with the better half tonight, and wanna give credit where credit is due here (and also clarify one misconception) - But this link by Kristi has proved to be most beneficial to me thus far... As you'll see, whilst it is 'clear as day' about what can, or cannot be done, it's also buried deep in UKBA's website as a sub-link to a sub-paragraph to oblivion and beyond... and it's no wonder I missed this before - Should be posted in large type on Page 1 .. But such is life...
That said, your premise is half right/half wrong - in that, yes, whilst visiting the UK to see the other half - I may go on to other countries - We all do this, and is part of being a tourist, or traveller, or 'visitor' - as I've not engaged in any of the 50 million 'restricted' actions that one is not allowed to do per the link provided... Yes, I do come for a few weeks to simply visit, and then leave - Simples (and I do stay on my own dime - I do not take any benefits - and I do not leech off the system) which I believe is their primary concern - So I think I understand UKBA's reasoning... And given the few scenarios I shared here before - I could certainly see why you (Kristi) may think I would/could overstay my welcome or make a wrong move - And it was right to advise me against doing something that possibly could effect my chances both now, or long term...
Now, all that said - what I did find interesting - were 2 of these 3 lines/conditions listed in your link:
(x) does not, during his visit, intend to marry or form a civil partnership, or to give notice of marriage or civil partnership; and
(xi) does not intend to receive private medical treatment during his visit; and
(xii) is not in transit to a country outside the common travel area.So it seems to me, that subsection "x" does preclude someone from going the spousal route... (if I'm reading that right?) ... So, to be totally honest, I'm not even sure now how you all did this (e.g. - you met your spouse via the internet and applied for a spousal visa here?) - technically, the way I read "x" - is that you cannot even do that? ... So, would like to hear how all you that did get engaged/married here - and which 'visa' were you under when you entered the UK, that did allow for that?
"xi" is not a big deal to me, for again, am in good health and not looking for care - but does concern me if I were to have a toothache or walk out in front of a bus or something - I mean, I carry international travellers insurance, which also is not cheap for emergencies abroad - but to tell me I can't get private care - is - well - silly

... but I also understand why they have to state this... Doesn't apply to me here today - so am not gonna stress about it (knock on wood) ...
Now, "xii" .. this was interesting -
"is not in transit to a country outside the common travel area" - Excuse my french, but WTF does this mean really?? Every person I know that has come to 'Europe'... lands at LHR, sees Big Ben, and then goes to Paris and a dozen other European destinations on holiday... So, I honestly don't see what they're trying to achieve here?? - nor do I really fully understand what it's allowing, or precluding? Either way, any of these; from me meeting someone here and us getting hitched, or slicing my finger open on a can - or me going to Paris for a weekend to see a 6 Nations rugby match (*cough*) - could all land me in hot water according to this... (all purely hypothetical, of course!)

Now - the other bit, was below that subsection, on extending ones stay - Since I've only run off a
few weeks of my allotted 6-12 months ... (I've never said if I was academics or sports or not) ... but either way, I see that I do have ways of extending, legally - and clearly, IF I were to ever 'do business' as a foreign entity here in the UK (vs. just coming here to see my GF - which even that seems to be illegal by subsection 'x') - If I do decide to do biz here - then 'next time' I go thru UKBA - seems I do need to declare my visa as general business, and not just tourist visa... I am NOT conducting business here today, so I'm not stressed about this - but IF we do decided to go that route (what now I guess is referred to as the T1 / entrepreneurial visa) then that's easily solved by making this declaration - and starting the entrepreneurial process... Simples - right?

RE: Credit - For those that have shared their credit stories -
Thank you for doing so - Those were also very helpful - and YES - most certainly, I can work and live and grow our existing business lines here from our US accounts/banks - but that then blurs the lines of 'intent' with UKBA - as well as those back in the USA (Chase for example, states clearly, that you'll only use your card for 'business affairs') - so - it's a double-edged sword of sorts... Plus, I wish to keep business and personal, separate if at all possible (for tax reasons, amongst many other obvious ones) ...
Either way, yes, I can live off those - and then start slowly bldg my UK credit over time, if we decide this is the way to go - The GF said tonight, that if we ever took the plunge, she'd just add me to her accounts - and we'd start bldg my history from that (which as hubby/wife, we are 100% legally able to do ) so is certainly doable as many of you have already said - But that was then that silly pride/ego thing for me... Why? I dunno ... I suppose it's the whole guy/male/hunter/gatherer/provider thing? ... I've always paved, and paid, my own way... and it makes me kinda uneasy riding her coattails - I know others do it - and by the sounds of things, I may indeed have to swallow my pride and do the same here with her... if we should ever tie the knot... I just have to make sure this is the 'right' decision for me, both financially, and personally.... as I am not 100% sold on becoming a Brit just yet (seen and lived in too many other great places - but do enjoy what many others enjoy here) - Humour being the biggest thing for me

... I love Brit humour - and can't live without it... Now, the 33*F and grey skies and rain for the past few weeks? that's a whole other story!!

It's akin to life in Cleveland IMHO... Hahaha - and I see no long lines forming to get into Ohio these days

)))) But I do like many things here... but there are other places to consider too... We'll see!!

)
Many thanks for those that have advised - and now I'm gonna go watch my F1 qualifying!
BB