Heartbroken and in need of advice

Im going to apologize before hand because this is going to be long, and probably seems like I long run on sentence but that's just me state right now. I'm not sure we're to begin so... I really need some advice. I'm confused and having a hard time understanding what it currently going on in my marriage. In October, my baby sister( whom has a mental disability) had a baby. My mom and step father have been his soul care takers since his birth a my sister is not capable to take care of him. Long story short, things have gotten to the point to where my mom may need to have my sister committed, and there was a concern discussed about my nephew being taken from her( my mom) with that happening. I explained to her in the rare circumstance of that happening that I would speak to my husband about my nephew staying with us for a short period in time until my sister was straighten out where she needed to be. When I discuss this with my husband he responded, similarly to the way he had in the past, saying that my family needed to stopped depending on me and that my mom needed to make my sister take responsibility for her son. He has always seemed to have an issue with my mom and mostly because he disagrees with her parenting, and he has always be direct in not wanting me to help my family. This time I have enough, it's been very stressful the past few months for me, and I told him how it made me feel. His said his concern is that I'm going to leave him and my kids to go help me family because we are so close, and that there comes a time when you part ways with your family and stop relying on them, I disagree a a ive always been close to my family. I thing is im scattered inside right now that one he would even consider that and two because I feel he is trying to make me choose between my extend family and my household family. Any advice is welcome, as well as if you need more info please ask