I think it's easy to say to do what you said what you would do back then.
I don't think it's that simple though. Yes, it's nice to be honourable and be a woman of your word. And yes, you feel guilty for the way things happened.
But before you draw a line under everything, I think you need to work everything out on paper. Debts you built up together, money you put into the house, money you would have otherwise spent on rent, money that he has saved by having you contribute to the house and bills, and so on. I'd also see if you can remember what the joint debt money was spent on - was it house improvements, furniture, holidays, car for joint use, or just living a bit beyond your means - and was that one or both of you, spending money on essential stuff like food, transport to work etc or did one or both of you like to spend on nice clothes or booze or a hobby or whatever...
If it was genuinely joint debts then fine. If not, figure out approximately how much the split was between each of you.
If it was more on one side (or influenced because one person had more expensive tastes in say holidays and the other went along with it), then adjust accordingly.
Then look at how much the house has appreciated over the time that you were together and subsequently. Would you have been able to save for a deposit or buy a house if you hadn't been paying rent/mortgage to your dp? If you would have been, why should you suffer so significantly financially for splitting up when things were obviously not right in the relationship for you? Would you have been so keen to let him keep any profit if you'd broken up and then had a new relationship afterwards?
You've already said that your friends think that your ex is friendly with you so he doesn't have to pay you more.
At the time, everything would have been very raw, I can appreciate that, on both sides. Did your dh ever get any legal advice at the time? Or did you? Who suggested it would be a good idea to avoid lawyers? Did you have any inkling of the amount that you would be walking away from or did you think that the debts that your dh paid off would approximately equal the amount that you were entitled to from your contributions and from having been married?
Do the sums, work out how much you would have been entitled to if you'd taken everything you were entitled to at the time of the split (after debts were taken into account), everything you'd be entitled to now given that you're only just legally doing all the financial and divorce stuff, how much you have missed out on, what your position would have been if you'd been paying normal rent (eg carried on renting where you had been if you hadn't moved in with your then dp), what a typical property would now be worth if you'd been able to put down a deposit and get a mortgage if you hadn't been with your dp and so on.
Only after you've got all these answers can you begin to decide whether or not you want to ask for any money from your ex.
Remember that it's all very well being upright and honourable and keeping your word - that works when everybody is behaving the same. But if there's any chance that your ex knew exactly what he was doing when he suggested that he would pay your share of the debt (so £5K assuming they were genuinely equally run up together) and that you'd feel so guilty that you wouldn't go after the £50K or whatever it might be that you would be legally and morally entitled to as a result of being married, then I think you should go after what you were entitled to.
There are way too many posts on MN where people have got divorced and in the interests of staying friendly or not running up big legal bills etc, they haven't used a solicitor (or have had the misfortune of using a bad one), and have ended up severely out of pocket and scrimping to get by for many years to come while the ex is laughing all the way to the bank. At least work out what the figures are so that you know in advance how much your ex has screwed you out of if that is the case for you too.