I have so many thoughts on what Bertholdt's home life must have been like. We know 3 things about him, and those are:
He has a dad, but no mention of a mom.
There were implications that his father was ill and needed medicine.
His dad was willing to make him a warrior.
This will all be speculation, since these are the only things we know. Also, I am not a mental health professional, so I may get things wrong. Anyone is free to correct me. Anyways...
Bertholdt as a character lacks confidence and a will. He goes along with whatever people tell him to do without thought or question, even when he is shown internally disagreeing with the final decision.
He also tends to fawn or freeze whenever there is conflict.
It is also likely he has an anxious attachment style judging by how he lacks boundaries, his anxiety, and how he prioritized Reiner's and Annie's needs over himself at times (he could never stand up for himself, but he always got angry on their behalf).
Combining the three facts we know above with Bertholdt's behaviour. There seems to be a common pattern that these traits come from people who grew up in a household that was either emotionally neglectful or inconsistent; experienced instability (such as death, illness, separation, war, divorce, etc.); were overprotected; had an authoritarian parenting style; or when the boundaries of the parental-child relationship had been crossed (i.e., A child takes on the responsibility of an adult). Instability and blurred boundaries seem to be the only ones that I can say are completely factual, as Bertholdt became a child soldier/breadwinner due to his father's illness.
I feel like it is also safe to assume he experienced some form of neglect, whether that was intentional or not, and an authoritarian upbringing. I do not think that it was purely Marley's fault due to the extreme nature of his behaviours and how there is a trend with Reiner and Annie, which may also reflect with Bertholdt. These two grew in a single-parent household with selfish parents who put their own needs/desires over their children's well-being. Sure Karina and Mr. Leonhart loved their children (to an extent and in different stages of their lives), but they also saw them as tools, a means to an end. Whether it was revenge, honour, or a comfortable life, they made their children into soldiers all at the expense of their child's health, happiness, or lifespan.
Although there really isn't much evidence on how their relationship was like, I do believe that Bertholdt's dad loved him, judging by how he calls him "old man" in his character song, the fact he was the only warrior crying when being forced to leave home, and how Karina talks about how often Mr. Hoover proudly talked about his son. It also seems that Bertholdt at least had positive feelings towards him. Though that may not be saying much since Annie loves her dad despite the physical abuse.
The fact that he became a warrior just for his father's well-being and how he is quick to resign to fate and what others tell him to do makes me believe that despite that love, his father raised him in a strict manner.
An authoritarian household makes sense with Bertholdt. A household where a child is meant to follow rules without question, shamed or punished if otherwise, with little to no explanation on how to do things would inevitably create a child who feels as if they are unable to make choices on their own, be fearful/shy towards others, associate obedience with love, and lack the social skills to form healthy relationships with others. It is easier for Bertholdt to do whatever others say and apologize when he doesn't meet their expectations because they know what is best and what is right; even if they don't, it is better to follow rather than be scrutinized or punished for disagreeing. He is willing to put all his trust, value, and worth on others as a result, even if he is unhappy.
As much as I love RBA, it is undeniable that their friendship is toxic; to no fault of their own though, asking for a healthy friendship between 3 traumatized, mentally ill, and abused child soldiers on a deadly mission is practically impossible. They definitely loved each other, but the stressful situation and the lack of a foundation of what a healthy relationship looks like made it hard for them to express that love. All three hurt each other because all they knew was to survive, whether it was through violence, dissociation and compartmentalizing, or fawning. Due to this, it isn't really a surprise that almost all of Bertholdt's relationships were unstable.
This is also adding to the fact that Bertholdt became a warrior for his dad's health, making him the breadwinner of the family; the underlying message of that choice is that he must sacrifice himself (mentally, emotionally, and physically) for his father's life.He will never live past 24 years old, but that is okay because it is for someone he loves.
This effects his relationship with Reiner and Annie. Taking care of Reiner's mental state despite his own suffering and trauma is okay because it is someone he loves. It's fine that Annie and Reiner are emotionally unavailable and that he has no support, because his needs are not important compared to everyone else, so he will gladly shoulder the stress and pain for others if he needs to.











