Sadness about the process

Dear everyone,
The reason I'm writing is that I have something on my mind and I have no clue what to do with my current feelings.
My partner and I have been in the medical process for over a year and a half now, and right now we're doing IUI. I'm finding it quite difficult, but usually I can put things into perspective. My partner has two sweethearts with his ex-partner, with whom the divorce went quite awkwardly, and our contact is always a bit tense to some extent, but we see each other regularly during the exchange times for the sake of the kids. Because of that tense contact and my partner's conflict-avoidant nature, almost all announcements are made very carefully to avoid any 'drama'. For example, she was practically the first to know that we were getting married. Just to not put anyone on the spot, but also so she had time to get used to it before the kids heard about it.
The ex is aware of our fertility journey, because this came up once back then and we thought it was important to be open and didn't want to have to lie.
Now, last week we went to pick up the kids together and they ran outside, super excited, with the announcement that they're getting a brother or sister. I didn't know where to look. Of course, I didn't let it show and congratulated everyone, but the look in the ex's eyes when she realized I had already heard... I can hardly describe it as anything but triumphant.
My partner and I remain extremely positive and enthusiastic about the news with the kids, but I find that I'm struggling with it in some way. They don't owe us any explanations, but I felt pretty screwed over because I had to strike a pose on the spot. That I got my period that same morning and it became clear that this cycle didn't work out again probably didn't make the feeling any better, but now, a few days later, I still feel completely knocked off course.
Does anyone recognize this feeling?

Love