Hi Tam, I had a bit of a yucky Valentines Day last year. However, this year I'm hosting a dinner party for six friends from my Divorce Support Group and looking forward to it.
First thing I would do is decide to have the 'best day possible' given all circumstances. Absolutely stay away from the phone that day and expect not to hear from your X at all. Then have a think about filling the day. Is there a single girlfriend who might want to catch a movie or something? If you don't meet up with anyone, perhaps spend the day 'loving yourself' - doing some things to show yourself love - have a nice bubble bath, read your favourite book, buy a new top, cook your favourite meal, have a pampering session. Like all antiversaries, it will pass and Monday is another day.
As for the baseball game and without reading back - presumably your X has OW around your 15yr old already? I would not ask him anything about OW - she is not worthy of your attention and is your X's problem. As you say, he would do what he wants to anyway - and probably tell her you didn't want her there - which makes you look like the bad guy. So, you don't get to control him, but you do get to control yourself. If she does turn up, you can breeze past and say Hi, looking radiant and leaving a faint scent of loveliness in the air. You can chat to friends after that, and laugh, having a lovely time - and leaving your X to wonder at his madness in leaving such a lovely wife for grotty OW.
For this, I think you need to grow a very strong spine, and be in no way intimidated or embarrassed by the situation. If he has embarrassed himself by his behaviour, or by bringing OW to the game, that's on him and is of no consequence to you...your 15yr old is playing and you are there for them.
JMHO of course, and I hope you manage to have a nice day on Sunday xx
T 13 M 7 Me 48 H 46 SS 15 BD 7.14 PA D final 5.16 (H filed)
We receive & we lose, and must try to achieve gratitude & embrace with whole hearts whatever of life that remains after the losses - Dubus