My Fiancé’s baby mama (HELP???)

So today is Mother’s Day of course, my fiancé hasn’t had anything to do with the mother of his children since we got together about a year ago. I think..... I mean anytime she comes up, he is totally or acts totally disgusted by her. Anyways. She text him on Friday and said that she was going to stay at her girlfriends house Saturday night and that he could stay at her house with the kids on that night. He told me he wasn’t going to do that, that he would go get the kids and stay at his house. Saturday night he ended up staying at her house instead of what he told me he was going to do. This morning he and the kids went to his moms for a little bit. Then he said that his ex called and said she was back home and ready for the kids. So he goes to take the kids back there. He has been there alllllll day long and just went to pick her brother up from the airport to bring him back to her house. Currently still there according to find my friends... How should I feel about this? Like I want to understand, because it’s his kids and we don’t have kids together, but like really he has been with her at her house all day without me. Is that ok?


(Let me add that he and I have the kids majority of the time. She didn’t even want them on Mother’s Day until last minute. I am unable to have children due to some unforeseen events as a child, so I will never “understand what it’s like to have kids of my own.” However I do love and accept his kids as my own and have done everything in my power to make them feel loved, accepted and all of the many things a mother should make her kids feel. As well as took on financial responsibility.)