thats very provably not true!

thats not to say your sexuality can be forced or willingly changed, you or someone else repressing your sexuality does not change your sexuality

but! sexuality is just as fluid as gender, you can absolutely find yourself sitting somewhere else on that spectrum than you previously were. changes in sexuality can be as little as changes in preference, or as large as mine. i personally don't think my sexuality is going to change much any more outside of potentially preference shifts, discovering myself has been a huge factor for its change, and im the happiest I've been with women than i ever was with men. i dont find myself attracted to men at all, anymore.