He was shown to be attracted to women since the beginning
Dude, a) there is such a thing as being bisexual, b) In real life, people have suddenly realized they're gay--and not even bi, gay--only incredibly late in life. Including people with grown kids, and who had never even questioned their heterosexuality before. Living in a heteronormative culture makes it real easy for someone not to be fully aware of their own preferences, so reading their inner-monologue(and not even 100% of the time) isn't exactly a perfect indicator no matter how long-running the character is.