That is true Lookout but we all make mistakes in this life and Colin was young and obviously not very emotionally aware.
I do think to have one child murdered never mind two is a massive nightmare which is impossible to ever recover from completely and Colin is no more guilty than many other young people who for whatever reason don't make good decisions or cope very well.
It's likely Colin didn't want to marry Sheila and was coerced into it. Back then even in London never mind the deoth of Essex countryside, a couple expecting a baby were expected to marry whether they wanted to or not, it was still a time of shotgun weddings. I would imagine Sheila was very difficult as she possibly already had unrecognised signs of schizophrenia, we know she had a violet temper. I see what you're saying but I think Colin deserves more understanding. 
Maggie,it's probably that I've seen/met a lot of " Colins " in my line of work which makes me feel so bitter. I've obviously taken the sides of the patients in the past and have shared their tears too. It's something you don't forget,ever,especially,like Sheila,they think the world of their partners and are set for a lifetime----------------that doesn't happen.
I think of Sheila when she wanted " another go at her marriage ",thinking that she and Colin would get back together. That alone is earth shattering when it doesn't happen,and with some who can't hack it,it's the end of their lives. It's very very upsetting,but NOBODY understood.