Oh do catch up! I think that was pretty much well established in
The Doctor Dances - back in the Eccleston days.
I don't watch the show these days - and I have distinct memories of watching now 'lost' episodes back in Troughton's time - because I don't watch ANY TV these days and, though
Doctor Who was one of the last shows I did make a date with, I stopped watching it because I got so fed up with the character being (as
@thaddeus6th so wonderfully put it "Space Jesus [who] is effortlessly and inherently special".)
As for mutable sexuality. Sexuality is mutable. I knew women who were separatist Lesbian teenagers back in the 80s who are now married to men, married men with grown up children who left their wives for other men, transgender women who love both men and women, (no transgender men - that I know of). For many humans sexuality is not 'fixed'. For many it is. The Doctor is the least 'fixed' character in fiction. The Doctor regularly (willingly?) changes their body ("HMmmm, new teeth!") and their entire personality. Why not their sexuality too? (Hmmm, new urges!).