I've quoted this because it strongly reminds me of an ex.
I used to be with a woman who seemed to value her time with her children less and less as our relationship developed. I'm not a biological parent although I have parented more than one child. I found her attitude distasteful to say the least. She would want me to be at everything and when I did attend, it quickly changed from us doing something with her children to her children tagging along with us on our date. Even events where we were only there to watch her children do something revolved around us, or should I say, me. She stopped enjoying being their parent and it was clear that she started to view them as burdensome because I didn't always want to hang out with the children and be part of their activities and instead of questioning our compatibility, she became resentful towards them. It was really off-putting for me. She probably still maintains that I dumped her because she is a mother. That isn't the case at all. I dumped her because I couldn't stand to see how little validation she got from her children, and how much validation she got from me.
I don't understand this. You didn't always want to be with the children, but you thought less of her because she didn't always want to be either?
If she felt you pulling away I think it's normal to end up focussing for a time on her relationship with you. We're human, we can't do everything, sometimes we need to firefight and focus on the relationship that needs our effort the most right now.
I love my kids, I home educate them, we're together almost all the time and I miss them when we're not but still when my husband and I have issues to sort out or need time to reconnect and nurture our relationship the kids need to take a back seat. Likewise, if one of the children is struggling then my husband needs to manage with less of my time for a bit.