You can change your mind about the meeting.
My ex swings between extremes: horrible, verbally abusive, paranoid behaviour on the one hand and overly-friendly lets spend time together watching movies, wanting to give me hugs, chat about his life on the other.
People who split up and have to remain in contact for the sake of the children often have difficulties negotiating the new relationship and it takes a while to settle down. Add into that on-going addiction, and everything that goes with it and that is a thousand times harder to get into an acceptable rhythm.
I don't want to be his friend and I don't want him to be mine, not at this point, I know all he could handle is a false friendship entirely based on his needs and perceptions, and that if I put a foot wrong in his eyes (any boundary enforcement or stating at all) he swings back to verbal abuse.
All I want is the basic civil interaction I would have with anyone else, a sort of business acquaintance: the business being raising our children. I don't want to watch a movie with him (we don't like the same movies anyway), or chat about what he's been up to over the week, or how tired he is because he "had to" sit up til 5am playing computer games online.
I don't divulge any info about my life (he doesn't ask, except to try and find evidence for the boyfriend/s that he is convinced I have), I try and limit contact, because the more time I spend in contact with him the more I have to repeatedly enforce boundaries and that sucks my already depleted reserves of patience/time.
I rarely bother stating my boundaries to him, as they always go unheeded, or he tries to argue me out of them: I just cut short the contact. My boundaries are pointers for me which cut down the crap in my life, not rules for him to live by; he's not a toddler, it's not my job to teach him how to behave.
Where possible I do everything by email, and I ignore any content that is not strictly business and civil about the kids/divorce logistics. This often means I write a big angry reply and sit on it for 2 days then chop out all the emotional stuff to a couple of simple sentences, or delete the whole thing.
It's by no means perfect. There are still times I let it get to me, in general those are when I'm already running on empty: I find it particularly hard when he's being "nice" (inappropriately over-friendly, wanting to spend time with me etc), as he won't take a simple no for an answer and badgers me. I haven't perfected the boundary holding in this situation as I still feel bad if someone comes asks nicely and then has hurt feelings if I say no. Even though logically I know that their feelings are their responsibility, and if they can't accept a civil "no" then it wasn't really a request it was a demand dressed up in nice words, followed by a lot of pressure.
In fact my ex’s MO appears to be that if he thinks he is slightly out of order with a demand, he'll go in guns blazing "attack being the best form of defence" and all. If he feels completely entitled he will ask nicely, but it never occurs to him that anyone could/would/is entitled to say no, so he is mystified, and very affronted when they do. He thinks the very act of asking rather than taking means that everyone will acquiesce.
sorry, I've used your thread to work through some stuff from the weekend: good luck, it ain't easy!