I think -
He went off with an OW after she issued a Christmas/New Year ultimatum.
He was living with her rather comfortably, maybe going on holiday (the tan) until she saw sense. Probably because he was living off her, being jobless. It all fell apart and she kicked him out.
His mother and some friends knew.
The police did what they could, found him and told you he was safe and well - but could do nothing else because he told them he did not want you to find him. This is sadly the right thing - how many people are escaping abusive relationships and get away? They have no way of knowing why he left. I'm sorry.
All his job could tell you was that he no longer worked there.
This was planned and executed intentionally with zero thought and respect for you and the children's distress.
Problem now: No job. No money. No home. No woman.
Solution: You! Expected to open your arms and everything else and welcome him back.
Stay fucking furious, love.
Solicitor. Get a clear sense of your and your children's rights.
Find out exactly what child maintenance he owes you having abandoned the family he has stopped supporting
I'd also send him a clear statement of exactly what his actions have done to you and the children.
I'd also be inclined to say you require:
A list of where he was living and when and who with
How he was supporting himself
Copies of all the bank and credit card statements
Maybe get your solicitor to send that.
He will refuse, lie, bluster, smoke and mirrors.
You need a business meeting with him, not the children and certainly not his mother. Do not allow any wheedling attempts to rekindle romance.
Do not listen to any attempts by his mother to cajole you into forgive and forget. Her status as grandmother would be her main thought, not your wellbeing.
Because if you have him back, he will do it again. And the damage to your children and to you will be lifelong.
When you can, some therapy for you all (not him) would be wise.
LTB.