OP
I can see it's not a great position to be in, but I think you need to be sensible and realistic.
At best you have been naive, at worst very foolish. Your boss could not instruct or enforce your co-workers to "pop out from work to get you" or collect you on their way to work solely to allow you to have a convenient commute! I cannot believe you actually thought that a reasonable thing to demand (unpaid) of your colleagues. I'm more surprised they all agreed to it though. Did you have any of this in writing or was this a throw away comment?
To be honest, I'm not surprised your colleagues have started saying no- it's disruptive if they have to leave the office to go and collect you. If they have to collect you on the way to/from work it's an inconvenience. Also- if your colleagues are using their own cars have you ever contributed towards their costs if they are coming to collect you? That's 3 miles per day, every working day (15 miles per week)- added up over a year, assuming 6 weeks annual leave, that is 690 miles per year..... But hey, they're saving the parking costs so they can afford to subsidise you....
Back to practicalities: I would have thought a move of 1.5 miles would be unlikely to trigger any relocation package or redundancy, unless there was a specific clause in your contract relating to that. If you have been there less than 2 years I don't think redundancy or constructive dismissal legislation applies to you- I could be wrong on that one though.
I would not think it reasonable to demand that your employer remain in the original location solely for your benefit (I'm not clear if that is what you think). I would also say that it is not your employers responsibility to ensure you can get to work, that is up to you. I would agree you should seek help from those organisations that can provide support.
Finally, with regard to where you go from here: you need to speak to your employer about reasonable adjustments. I'd advise you to do this after having talked it through with your union representative.
Note that what constitutes reasonable adjustments depends on the nature of your work, the size of the business, the impact of your proposals on the employer and so on. It doesn't mean you can unilaterally decide the terms of those adjustments- e.g. you cannot announce you will now be working from home on x days or only working 25 hours per week when you are contracted for 37.
And if you reduce your hours, I think you will have to accept reduced pay- how you can think it reasonable to reduce your hours (? by three hours per day, so if working 5 days per week that would be 15 hours) but expect full pay I really don't know. It's also massively unfair on your colleagues- you get paid the same as them for less work. And presumably someone will have to pick up the work you aren't doing when you aren't there?
If the reasonable adjustments that you want cannot be made (assuming you are not able to challenge that), you'll have to look for a new job and do the commute until you start that new job- or as long as you can, and then if you become too unwell to work you can be signed off. Or you can hand in your notice now. You can't just start turning up late or leaving early without the agreement of your employer- unless you want them to dismiss you. But I would have thought that your poor time-keeping would show up on your references, which wouldn't be helpful to you in the long run.