PTSD might have been a reason for his depression since he was in Iraq and the events from that time might still haunting him. But there is help, as you stated, and weapons should have been kept away from him, although sadly to say if a person wants to take his own life there are other possibilties.
I cannot imagine that starting a family, Ella being 42 by now, would have caused the problem. They had been married for almost 5 years , discussions about wanting to have children or not would have been settled long ago, never ever would just that fact, moving to a bigger house and starting a family cause somebody to take his own life.
While we might never know what cause this sad tragedy, we also don’t know if the family building had anything to do with it. It’s not any of our business if they actively chose not to have children or if getting pregnant was something they were aspiring for but perhaps wasn’t working. But if they had been trying and were going through infertility, there have been a lot of studies from the UK on the mental health impact of infertility- nearly half of patients going through infertility have experienced suicidal thoughts and 10% have them most or all of the time (Fertility Network UK’ statistics)
While this might not have anything do with Thomas, the way that some of the news surrounding them (I read an article that said “they remained childless”) did make me wonder. Even if not, as someone who went through years of infertility I know it can have a huge impact on mental health. I hope this wasn’t the case for them, and had actively or positively chose not to have children, because infertility struggles are awful.