IME this is all about mindset.
If you can't afford it today, you can't afford it tomorrow with interest. You logically know this, so you know you're doing yourself a favour to stick to it and not run up debt.
Understand that sometimes others don't feel the same. Some people are irresponsible. Some even have the mindset that they'll die before their debt is paid off ie it is their intention to never pay it off. When looking at what others have, remind yourself that a lot of them haven't paid for it.
If disaster falls, an unexpected large bill or redundancy for example, it's those without debts who will cope best (leaving aside the issue of the stinking rich who can throw money at any situation that arises in life).
Practice gratitude and you'll find a greater degree of contentment. Eg, you and your friend both need a table. Your friend goes to the shop and buys one she likes even though it's not the cheapest. You can't even afford the cheapest one in the shop or any shop. So you look in the charity shop, or second hand sale, or you find one abandoned by the side of the road. Maybe it needs a little fixing up, is a little wonky or needs a lick of paint. You can at least clean it, with whatever cleaning agents you already own. You needed a table and now you've got a table. It might not be perfect but your life is improved for having it. No use looking at what you can't have, look at what you do have and be glad.
Get used to bringing your own food and drinks with you. Don't treat yourself to a coffee every month, save the money up and treat yourself to a cute picnic bag, so you don't feel like a tramp carting your lunch around in a battered carrier bag. You can smile at its cuteness as you pack it in the morning, knowing you're going to be able to fuel yourself throughout the day and not having to go hungry or thirsty. Instead of sighing at its tattiness and feeling "less than", if you're packing a battered carrier bag.
It's priority. Alter your perception of who you are. You're not someone who buys shop made sandwiches. You're someone who is organised enough to make your own, with healthy ingredients to nurture your body, it may have come out of necessity but is actually a good thing. The only thing you're denying yourself is junk that's full of preservatives.
You maybe don't go out much but maybe you could go out more if you wanted to, it would mean eg rehoming your dog though. So you're choosing to stay home instead, because your dog means everything to you. Sunny days are free and you enjoy your dog walks and the people you meet during them. It's a lifestyle choice, are you eg a weekend drinker or a dog owner, what means more to you?
Things like that. We all have our income, from whatever source and whatever the amount. We are in charge of our own priorities and what we choose to spend it on. You can have (a version of) most things. The question is, are you prepared to give up whatever it is you'd need to give up in order to afford it? Don't think of it as denying yourself, think of it as choosing differently.
You might not have many clothes but if chosen carefully, wherever they come from, you can ensure you love every one of those items and enjoy wearing them. Focus on that, not on all the things you'd like but can't afford. Step away from society's expectations of a constant stream of new new new. Whether it's clothes, décor, cars, hobbies etc. Look to what makes you happy and prioritize that.
If you're achieving a home that's clean and relatively tidy, if you're warm enough and not constantly hungry, if you're clean and tidy in your personal style, if you obey laws, love your children and have people with decent morals as friends, then you're a success. The rest is just details, optional extras. Don't spend on the details whilst ignoring the foundations. Even if all you have is the foundations, your life will be solid. Details only bring fleeting happiness.
This altered lifestyle and mindset probably needs different friends. If you don't fit with who you're surrounded by then of course you'll feel not great. I don't mean closing off old friendships completely, although in some cases it'll naturally occur where the friendship was based purely on convenience. A true friend will still like you no matter your financial situation, but realistically you're going to see them less, because your lives are heading in different directions and you're on a different path. It's natural. There's others on your path though, connect with them. Going to the park with the children won't feel so bad if the other family can't afford the ice cream van either. You can still have a good time without ice cream.