I'm not sure that I have any good advice about how to deal with this difficult issue - except to say, make sure you get clear about what buttons he's pushing here.
I got the impression from your first post - that what you are really upset about is that he is chopping and changing arrangements, at a whim, and by text.
It would seem reasonable for you to want to discuss those arrangements face-to-face or at least over the phone rather than by text ... however, if this is a one-off, does it matter? Is it worth dying in a ditch over.
The threat of 50% custody is interesting. If he doesn't like having the car seat in the car, goodness knows how he's going to go with 50% time!!! (little laugh)
You did seem a little bit defensive in your texts – and I SOOOO understand that. But, sometimes, less is more, and sometimes you collect more bees with honey than with acrid smoke.
What I would do is backtrack a little bit. Perhaps call him and say, lightly, and with a smile in your voice, something to the effect of “wow, that got out of control quickly. Look H, this is tough stuff for me. I am defensive about it for a whole range of reasons, but mostly because I would like some certainty and consistency for S3 and me. It would be great if we could figure out a way to communicate with each other about S3 that takes into account his needs and both of our schedules. I’d prefer not to do this stuff by text, because there’s too much room for miscommunication. I mentioned a mediator, because I’m feeling a bit powerless in this parenting relationship at the moment and sometimes it feels to me like it’s all your way. I understand that’s my perception and perhaps not yours, but we are talking about our son here, and as you point out – he deserves the best of both of us.”
Do you think the 50% custody thing is something he really wants, or something he knows will push your buttons – his comment about “I know you don’t want that” is telling – because who the heck is he to know what you do or don’t want??
Just look after yourself girl. Remember too that you don’t need to respond to him immediately when he texts. You could ignore them, or just shoot back a quick one to the effect of – thx for SMS. Let’s talk. I’ll be available to chat at X time tonight. ???
I don’t know Red … go with your gut, try to take some of the emotion out of it, try to be rational and calm in your discussions and remember that you are a super-fine-sister – and whatever happens , you are going to be OK.
(((chin up))), V
V
Never make someone a priority, who makes you an option.