Just catching up on your thread and I have to say I've had similar ruminations about things. Sounds like we are both in similar places emotionally and mentally.
Thanks for checking up on me. I posted an update under my thread when you have a chance to catch up. Regarding the birthday party for your D8, I'd consider just doing your own BD party for her, especially if you have family and/or friends in the area. I don't know if I posted or not my recent experience in December with my W over D4's BD party. Basically the kids and I had a very modest BD party for D4 on her actual birthdate as they were all staying with me at the time. My W had agreed to throw a "full" BD party for D4 that upcoming weekend at her place and I was invited. My W's turn to take the kids was the night before the party. The following morning, I wake up and call my W to see what she needs me to bring to the party and she informs me I'm not welcome at her house for the party after all because of my celebration with the kids earlier in the week. It was complete BS and a total power play by my W- at the expense of my D4. Needless to say, I learned my lesson.
I don't know what your STBXW has in mind for your D8's BD party, but no doubt she has her own agenda and it probably involves either showing you up (i.e. outspending you on gifts) and/or making you feel bad and/or uncomfortable. What if she uses the party as an opportunity to show of a new boyfriend? I know that thought probably hurts, but it may not be outside the realm of possibility.
Without knowing more, I think my vote would be for you to have your own BD party for D8.
M: 41 W: 39 S: 11 S: 10 D: 4 1st contact w/OM: 1/19/09 EA began: 2/14/09 EA discovered: 3/1/09 I file for D 8/25/09 to protect myself _______________________________