Why do offenders keep putting their children through this?

Hello Prison Widow. I would appreciate it if you could sign me anonymous. 
I have 2 children age 5 and 7 and their Dad is in prison for the 3rd time. I don't want a life of prison visiting for my kids and I am fed up of the prison relationship thing. Every time he goes to prison he says he'll never go back inside but he always does and it distresses my kids. It's not fair on them and although I think the kids have the right to see their Dad, I am fed up of this never ending circle and tired of visiting. It's not fair him putting the kids through this and I don't want my kids growing up thinking this is OK because it's not OK. I feel like I am stuck in a catch 22. His parents refuse to visit him so I have no one else who could take my kids to visit him. My friends won't take them because they are angry he is putting his children through this and I agree with them. I know no one can make the decision for me but why oh why do offenders keep doing this to their kids and families? Yours Sincerely Anon.