Hi Candy, so glad to hear that you are starting to get things sorted. The others are giving you some super advice on how to manage your ex. All I would add is be true to yourself and don't allow him to worm his way back into your life. You don't need him, and if he had any regard for you and your children, he wouldn't have behaved this way. You and your childred deserve millions better, and when this is all over, you will one day get it.
Hope the dental issue clears up too, tooth ache is so ouchy, you have my sympathies.
You also mentioned that you received a letter from the council that you didn't understand. I was made redundant last year, and know how complicated the benefits system is. Rather than worrying about it, why don't you give them a call tomorrow and ask them to explain the contents, and ask them to clarify what action you need to take next. To organise my housing and council tax benefit, in the end I called the council helpline and they talked me through it step by step to ensure that I got anything I was entitled to. Don't be afraid to ask questions, these people are paid to support you.
Finally, I hope you have been able to get your ex to sign the letter to remove him from the tenancy agreement. If he point blank refuses, the next step would be to ask the council to help to rehouse you. Given your circumstances, I feel sure that there will be help available. I know it would be hassle but a new home, may help towards a new start for your family.
As ever, my best wishes for you and your family, fingers crossed things will improve very soon. Oh and keep posting, there's millions of support for you here. Consider us, your own personal cheerleaders.