I think you need to get real specific with her as if she is an unstable potential enemy who you need to still get along with. Not pushy, just specific. Lack of specificity contributed to the solicitor, "if that's how we're going to do things", turning into an option that was available on one day only without warning, turning into a divorce filing and solicitors. Yow.
So my advice is write back to her. Tell her along the lines of "W, I don't know how you got the idea that I didn't care to see my kids because that couldn't be further from the truth. I went out of my way to let you have them last weekend because I thought that was what you wanted. I will work on a more specific agreement so we have a clear understanding, but until then this message will serve to notify you that I want to see them every single weekend. If special circumstances require us to make a change for a particular weekend, I will speak with you, or vice versa, at least 24 hours in advance.
You mentioned that you had made plans with them this weekend; I would like to accommodate this time but also would like my time with them too. Please let me know what times are available for me to see them this weekend so I can make plans."
I would get legal advice on the wording of an agreement that you would sign about custody of the children, but if you have been going dim/dark it sounds like she's prepared to use that as evidence that you are uninterested. You need to show interest pronto, don't wait until after this weekend. Good luck, she sounds extremely angry and punitive.
Adinva 51, S20, S18 M24 total 6/15/11-12/1/12 From IDLY to H moving out 9/15/15-3/7/17 From negotiating SA to final D at age 50 5/8/17-now: New relationship with an old friend __ Happiness is a warm puppy.