I was Protestant, converted to Roman Catholic, and then six years after became Orthodox. Whether I regret being Roman Catholic is difficult to say.
I don’t think I regret being Roman Catholic because it taught me a lot of things that I never had heard of as a protestant. It taught me the importance of and love of liturgy, history, tradition, saints, Sacraments, and other things.
However, if I had become Orthodox right away I would’ve been Orthodox six years earlier than I was and my college ‘career’ would’ve been easier to handle. I also would’ve learned all of those things above that I learned in Roman Catholicism.
But if I hadn’t been Roman Catholic I wouldn’t have been able to explain Orthodoxy to Romans in the (admittedly limited still) way that I can. On the other hand I wouldn’t have endured the six years of loneliness that Roman Catholicism…led to? Caused? I don’t know what word to use.
I was not the only Roman Catholic in my family, though I was the only practicing one. I had no Roman Catholic friends, and as almost every Roman Catholic knows community is very limited in Roman Catholicism. Nobody thought my beliefs were weird though. I didn’t loose any friends because of it - I just didn’t have any friends who shared my beliefs.
But the lonely thing, meh, I probably wouldn’t have noticed if I didn’t have my Orthodox life to compare it to. That is not what would’ve caused me to regret having been Roman Catholic. The only thing that could possibly do that is the knowledge that I could’ve been Orthodox six years earlier than I was.