Usually I do not regret things, still life is on and Almighty gave me everything, peace, life, and happyness so nothing to regret.
Say always Alhamdulillah.( With the grace of Allah.)
But I regret most taking a home loan on interest in my early days of job. ( long time ago- 2000.) Paid and settled. I regret because it is Haram (Prohibited ) in Islam to take loan on interest, I took and I paid for it. I lost my happyness after that, I got peace and happyness only when I get rid of it.