T not sure what a 'homecoming' is but I too have had STBXH turn up with OW. However in my case it was right at the beginning. He used to bring her to S17s rugby matches. Things got so bad that in the end S17 just stopped playing. It's such a shame b/c he had potential to do really well in this sport. S17 hated that his dad brought OW for two reasons:
1) Prior to him leaving me it had been thier time together. I used to turn up to watch the match but H and S17 went training together first. After OW turned up on scene H stopped the training bit.
2) It tore S17 apart to see me so upset. Given that this was within weeks of H leaving me I think anyone in their right mind could see this as a bad thing.
What strikes me about your XH is that he seems to be doing everything in a reverse order to everyone elses WAS
Me 43 XH 45 M 2.7.88 Divorce 7.10.09 Kids D20,S17 & D15