I just read your posts and I am so so sorry you are going through this, a whole life changing event in 3 short weeks. ((((hugs))).
I know you are getting legal advice, but I just want to ask you not to rush into anything with regards divorce or agreeing to maintenance yet, take your time to make sure you get the best possible financial and custody outcome for you and your kids.
I don't know anything about the legalities of divorce in the UK, but my friend has just gone through a divorce in the UK (H cheating with a work colleague, same old cliche) and her H was railroading her into accepting his 'very generous' offer of maintenance and living arrangement (nice new 2 bedroom apartment in her name, from the proceeds of their house).
In the end, she actually got a higher maintenance agreement than his 'generous' offer, a life insurance policy, private healthcare for herself and her child, the car, and she gets to stay in their current home until the child is 18, and he has to fund the mortgage, until then, when they either sell the house or she can buy him out.
It took a long time, more than a year to trash it out, and in the meantime he had to cover all her and their DC costs.
My friend and her ex were together 7 years in total, 4 of which were married, 1 DC.
He is a high earner, with a lucrative career ahead of him, so there was a high earnings potential to base the agreement on. While not knowing your DH's earning power, you should try make sure your solicitor works to get you the very best deal for you now, as there will be no going back once it is signed.
Take care of yourself and enjoy your evening out.