My fiancee's adult child is testing our relationship

Hello. I am a 51 year old widow with 2 grown children ages 27 and 31. Both are college educated, married, and self supportive. About 5 years ago, I started dating a divorced man, and we are know engaged. He has 3 grown children that still live in his home, ages 21, 25, and 27, they all have full time jobs. The eldest also has a 6 year old that lives at home with her. About a year ago, my fiancee moved in with me. He has not been helping out with our household, because his eldest child has relied heavily on him to help her financially (in addition to him still paying for the home that his children live in, as well as all of their living expenses) and with his grandchild (babysitting, taking the child back and forth to school and extra curricular activities, etc.) Recently, his eldest daughter began feeling depressed and posted some rather worrying articles about being suicidal on social media. I brought this to my fiancee’s attention, and now he has moved back to his house during the week to be more available to help his kids with household chores and babysitting. I hope this doesn’t sound like I’m being petty, but I will admit to being resentful. You see, this isn’t the first time that his eldest has had some sort of drama that requires her father’s and/or my immediate attention. In the past, it has been mostly money related, related to issues with a failed relationship, medical issues that later proved to be much more minor than we were lead to believe or perhaps even fictional, or issues with being able to manage being a single mother. How do I handle this? I feel like I am being taken for granted and basically cast aside all of a sudden because the daughter needs more of daddy’s attention. I really don’t want to end our relationship because of what I hope might be a temporary situation, but at the same time, I can’t see a future for us if this continues. Any advice? Thanks in advance.