Arthritic, hope your having a good time seeing your kids. Thinking of you.
lovetogive, I know exactly what you mean about choosing the times to challenge him. From my (allbeit limited) experience with a man like this, if you do start to regularly challenge things then they change their behaviour. But not necessarily for the better. My NSDP would sense me standing up to him and stat being really nice, only to revert back a few days later, once he'd hoovered me back in. Or he'd be even harder on me, laughing at me when I attempted to put boundaries in place. I remember him laughing at me scornfully when I told him one night that his door slamming and shouting was out of order as it was intimidating. Told me I was ridiculous and too sensitive. I never knew which way he'd go.
That all said, I'm still finding it hard to completely detach. Every time I see him, to drop our son off or pick him up, I get drawn into a prolonged situation. Sit down, do you want tea, how are you, can we talk properly, etc. I end up getting upset and I feel that I look weak, which perhaps is what he's aiming for. He wants me weak because then he knows there's a chance I'll buckle and go back. At the morning drop-off I was trying to talk again about the house situation, talk about my needs (after counsellor told me I'd allowed him to not meet them, with no consequences), but he was still set on staying. But instead of walking away from him and saying 'fine, if you wont meet my needs, I'll take that as an indication of your ongoing commitment to changing', I ended up crying and then asking for a hug because he was standing right next to me rubbing my shoulder. Kicking and shouting at myself in my head after that. Stupid stupid stupid. 
But yesterday evening, I saw my stepdaughters for the first time (have texted and spoken to them though, they're great girls), and we were chatting and having a laugh. When I was going, I was different to how I've been - more consciously upbeat, not wanting the girls to see me getting upset. NSDP was distinctly off with me. Spoke curtly. Looked at me funny, slightly intimidatingly. I could give him the benefit of the doubt and say he was feeling funky because he'd just woke up. 
Or he didn't like seeing me being 'ok' with everything and normal. Putting stuff in the car, I did ask him if he was ok (he does this silent staring thing where you feel he is waiting for you to say something). He said he was sad seeing the girls with DS, that they were struggling with the situation. I felt guilty. Which I suspect was the point of him saying it. He said a couple of other things along those lines. Then later, I got a text from him saying how he missed me, it seemed a long time till Wednesday till we see each other again. I know his MO by now, and knew that text would come. I replied saying it would actually be good to have space, not heard from him since...
Sorry, my posts are all ending up dead long because I don't get to post that frequently. Heigh-ho.
Keep enjoying the sunshine everyone. 
o'clock yet?