Immigrating to the UK (Manchester)

Hello All. This is my first time on this site and I'm searching for some answers to a few questions I have about immigrating to the UK. First off, I've been in Wales for the past 4 months living with my partner. He had come to visit me in the states this past October, but we have been together for almost 2 years. I am returning to the states to attend my granddaughter's high school graduation and returning to Wales after a months visit "home". My questions are: 1) will I be able to return so soon with no problem, no "special" visa? 2) Do I really have to go back to the US to apply for extended stay and be in the US for an entire six months will awaiting that visa? 3) Can the 6 month visa given to visitors be renewed easily if at all? I'm sure there are many other questions that will pop up for me along the way, but these seem most pertinent at the moment. I will be in Wales for another month, so I'm attending to get those proverbial eggs in a row before I head back to the USA. Thanks all, and any help will be greatly appreciated.