I genuinely believe Ruben's father set up a situation to "lose his virginity for him" like Ruben did for Niall. That his father would say and do sexually inappropriate things in front of him. All under the guise of "making him a man."
That, in combination with his time at the young offender's institute, definitely contributed to his skewed ideas of masculinity and sexual expression.
He went in at 15 and served two very formative years of his life surrounded by other offenders, who have no doubt been through similar situations as Ruben (if not almost certainly worse). I can't imagine what he survived in there. If it's anything like the juvenile corrections facilities in the U.S. he may have been sexually abused there as well, and almost certainly had to physically fight to protect himself for one reason or another.
As a result, Ruben is hypersexual. He has absolutely no boundaries when it comes to sex and sexual expression: practically dry humping Joanna in the middle of the flat, his lengthy makeout session with Celeste, grabbing his boner at the club, walking around the flat completely naked. It's all a way to reclaim the lack of control over his body and environment.
Also, I wonder at his mother's, and frankly, Niall's mother's neglect. They most certainly did not do enough to support his transition when he left the Institute and returned to school. Instead of starting a conversation and making Ruben feel safe, they swept his father's "visit" completely under the rug when the boys pretended they didn't hear it. They quietly ignored every one of Ruben's very obvious cries for help. They hoped Niall might rub off on him, instead of setting proper boundaries and helping both boys through the transition of his return.
All of this is compounded by the time period where in a lot of these ideas of masculinity, sexuality, and parenting were completely normalized. This idea that Ruben was ingrained to act that way rather than it being a product of the trauma he survived. The fact that he needed hands on intervention and support to allow him to become a mentally healthy and resilient individual who could grow and change.
Instead, he becomes an adult who now must choose to assume responsibility for his healing and growth or remain caught up in the same cycles of toxic masculinity, violence, and emotional repression.
