I think you are possessed of vast reserves of patience and kindness, certainly well beyond the amounts that your parents deserve to have lavished on them.
I have always believed in my children being independent, and spending time with me and their mum because they want to.
I am fortunate because all live near, but they all work, have partners and children, and busy lives, so I freely accept that their time with us is limited.
My responsibility for my happiness is entirely my own, and not theirs, and I would never visit my bad decisions on them with the sort of moral blackmail you are being put through.
Make it clear to your parents that you love them, and are keen to have them in your life, but they are part of your life, and by no means the main part, and they have to accept that. If they are lonely, they need to make friends and develop interests, not expect an adult family member to rum around making them feel better - it wouldn't work anyway, there is no pleasing self-pitying people like this.
You are entitled to your life - don't give it up to throw your time and enjoyment into a bottomless pit of immature neediness.