Responses
You are right but they usually use this plot in yaois to "normalize" liking same gender. It is like "he never romantically or sexually likes men but now he "have to" like them." In fact I refered to excessive use of this plot. Otherwise you are right, bad experiences can lead someone to different paths.
It is really annoying to assume that traumatic experiences decide the one's sexual oritentation as if being gay is psychological disorder but it is an ordinary set up for a yaoi storyΣ(  ̄□ ̄||) apart from this, they are a cute and lovely couple besides there is no rape, abuse, blackmail or evil side character ٩(๑❛ᴗ❛๑)۶ it is a good read.