Okay op, this is how I see it:
You are far from a failure, you are an educated mother of three firstly, and you are a survivor. That counts for a huge amount given what you have lived through.
You are still here hun, and I bet you are a brilliant Mum to boot! In fact I can hear that you are...because when you have experienced a difficult childhood you put so much into motherhood to 'make up' for what was lost and not there in your own.
Just a few observations.
I can't see anywhere in your posts that you have had some support with this. No counselling, no CBT why not? You clearly should be having this as a bare minimum.
You were a young girl, traumatised your 'father figure' came along and made you feel safe and loved. Why the hell wouldn't you marry him? You haven't ever felt safe and contented before, so he gave you stability and everyone sacrificed. You - sex and a youthful life. Him - childless existence.
So why blame yourself for this? You were vulnerable and he was there.
Fast forward to now, and you need to get some help, counselling and advice before you consider divorce.
Being vaguely unsure about what to do is dangerous to your long term happiness. Deal with the inside first, then tackle the outside and leave everything as it is in the meantime.
The city break should happen anyway, it will be a welcome break