I feel sad about this

My younger daughter is arriving this evening from out of state.  Here is something that makes me feel very happy and grateful:  My sister is hosting her overnight so that I don't have to make the three-hour round trip to and from the airport in the dark.  Here is what makes me sad about the situation:  My ex-husband not only spends less time with our daughters than I do but also spends less time with them than do my sister (their aunt), my brothers (their uncles), and my sister's ex-husband.  In what universe is this kind of parent-child relationship okay?  I know, that was a rhetorical question.  It's not okay.