Why am I experiencing parent guilt?

I grew up in abject poverty. We're talking no central heating, ice on the inside of the bedroom windows in a morning, all sleeping in one room because it was all we could afford to heat kind of poverty.

At age 8 I didn't know any better and it was only really in my teens when I did. I can guarantee that given everything you've posted that he doesn't feel he is missing out. He gets to do loads of after school activities, you take him on holiday. Only difference is you have a less expensive house than YOUR friends. Your house is the same as every other on the street so it isn't like in Charlie and the Chocolate Factory where yours is the ramshackle house sticking out like a sore thumb in a street surrounded by high price properties. No doubt his friends out of school are on the same street.

As for living in an ex local authority house, bargain of the century. I live in one, my last one was one. Until recently I owned two houses so when I sold the other one I could have quite easily gone and bought a nice new modern house on a nice estate. HOWEVER I've delivered building materials to said houses, I've been inside plenty, my brother owns one. Look nice, built like crap, the neighbours tend to be up themselves and god forbid you do anything to your property or do anything they don't agree with. On top of that the extra cost of the mortgage usually means less money to play with which is certainly the case with my brother who earns twice what I do but seems to be constantly skint.

No I reckon you're better off as you are living in a house you can reasonably afford and which has plenty of room and you're not working yourself into the ground to afford just to present some kind of lie to the world about how well you're doing.

You should look on the internet about the difference between millionaires and middle class when it comes to spending. The millionaires are the ones who live in modest houses and drive around in older cars because they would rather invest their money in something that makes them more money, not a depreciating asset or something to shout about how rich they are which costs them money. Hell even Warren Buffet the billionaire lives in the same house he bought in the 50s, drives around in a 2014 Cadillac XTS he bought new but which was an upgrade from his previous car, a 2006 Cadillac DTS, which he decided to get rid of when his his daughter Susie told him it was embarrassing. So if driving around in an 8 year old car and living in a fairly modest (by American standards) house is OK for a billionaire then it should be OK for you. On the other hand the middle class live in expensive houses and drive around new cars in order to flaunt their "wealth" but the reality is they have little cash once they've paid for it.

You've tried living a life you couldn't afford on plastic, how well did that work out for you? Obviously not because you wouldn't be here posting that. Now consider that your friends who've upgraded their lifestyle are now doing what you used to do. When you look at your friends and what they have ask yourself how they're affording to do it all given their income. Chances are they aren't, its all done on credit. At some point in the future they're going to be experiencing the pain you are, pain that you'll have been long free from never to repeat from the lessons learned. That thought alone should be enough to make you feel warm and fuzzy inside when the life you lead is one you can truly afford.

I would say kids at 8 are not expensive unless they are being educated privately. You don't have massive childcare costs of babies/preschoolers nor the cost of expensive school trips, gadgets useful for educational purposes or eventually driving lessons, cars, flats or weddings.

Your son does after school activities, he is housed, fed and clothed and you do holidays so you should not be beating yourself up over that.
the thing I would be more concerned about is your future as the debt stops you saving for things like University costs and saving to help him with flat or house deposits and yours and your wives pensions. You are addressing it though so I don't think think you should beat yourself up too much. I do hope you have restarted your pension contributions though as I seem to recall you stopped those last year.