There is more evidence to suggest there are genetic/biological reasons behind homosexuality than 'conditioning' or the likes, but nothing has been 'absolutely-confirmed'..
Nathan_Lane_Rules! though, it is quite a controversial conclusion to suggest Musical Theatre caused your homosexuality. The problem is you have no evidence to support your theory but the apparent correlation between homosexuality and theatre...
"You can't overrate Bernadette Peters. She is such a genius. There's a moment in "Too Many Mornings" and Bernadette doing 'I wore green the last time' - It's a voice that is just already given up - it is so sorrowful. Tragic. You can see from that moment the show is going to be headed into such dark territory and it hinges on this tiny throwaway moment of the voice." - Ben Brantley (2022)
"Bernadette's whole, stunning performance [as Rose in Gypsy] galvanized the actors capable of letting loose with her. Bernadette's Rose did take its rightful place, but too late, and unseen by too many who should have seen it" Arthur Laurents (2009)
"Sondheim's own favorite star performances? [Bernadette] Peters in ''Sunday in the Park,'' Lansbury in ''Sweeney Todd'' and ''obviously, Ethel was thrilling in 'Gypsy.'' Nytimes, 2000
Not many things are "absolutely confirmed" when dealing with how the human body/mind works. They still aren't 100% sure why most people are right handed, but a select few are left handed. Or what exactly causes cancer and some people develop it (esp those who live a "healthy" life) and those who don't. Weird.