You might find that a visit to your GP would help. Feelings of being alone, no friends, family don't care and poor libido might indicate something else.
I don't know much about the British Masters except that they have events about the country. Do they have social meetings etc. Travelling about the UK would not get you friends locally unless there were many runners in your area travelling.
It seems your thread is losing interest maybe the TV football. Loneliness doesn't seem to be something forumites recognise or want to discuss.
You feel apart from your family. Perhaps take all out for a meal/drinks say each payday. You make time for them and they may return that time.
No way give up your running if you did that and things didn't improve you might have nothing. Running will help keep your stress levels down.
You may be experiencing delayed mid life crises. Not a joke. In your fifties you have had some reason to look up and look at your situation and believe that nobody is there for you. Some people make a new start is that in your mind, would you really and I mean really be able to do so if as you think you have no friends and may be set in your ways.
I suggest keep what you have at present. Look more positively at people you know and/or meet daily. See each as potential friends, can we talk over coffee, meet for lunch, (runner?) we could meet up for a run on...., fancy doing the local Parkrun. You feel alone so perhaps think as a 'single' and maybe even find a girlfriend!!
I think you are doing O.K. as you profile shows only 25-30 miles a week. You are taking a 'scattergun' approach to your racing. Double ultras, Ironman thoughts, 4 marathons in 3 months, Comrades, Quadzilla, 38 marathons in 7 years your PB is 3:41.
What is your purpose in running? Is it to join the 100 Marathon Club if so keep doing what you are doing and you may succeed. If it is to improve your PB continuously as a marathon runner then you need to change your whole approach so look at your training, up your mileage 40-50 and run maybe only two marathons a year! Running marathons well is a big subject to cover but to run as well as you can will be your limit and that might well be 3:41.
Your PB makes you a mid pack runner some might unkindly say a good slow runner. It is probable that your body is strong but needs speed endurance added to your training and that will take time and dedication Speed is hard, painful and causes injuries. It will mean you need to reduce the number of marathons you run, maintain high energy levels and maybe test you speed endurance frequently in 5K, 10K and half marathon distance. Find out how long you can maintain say 7 minute miles and if the answer is 13 miles comfortably then you might just sneak in under 3:30 for a targeted marathon. In view of what you write I think even 4:15 in Edinburgh could be hard work for you with 3:41 as a PB.
I think our MP's are probably as good a mix as the general population. I don't think they all put themselves forward for Parliament for the expenses or perks, that is just silly talk. They have foibles and make mistakes as anyone does but they have to understand that they are answerable to the public who pay them. Like the general population there will be some crooks!
Certainly I do believe that some are deliberately chosen by their parties as highly suitable candidates for top jobs but to my mind that is no different from any other profession. I honestly believe that choosing someone because of the school or university they went to just does not happen as the bottom line is personal capability to do the top job under public scrutiny.