Pregnant sister, need advice! Please comment

I (21F) just found out my sister (31F) is pregnant. She and her husband have good jobs, are completely responsible and capable of having this baby. I have just graduated college and moved home (about 20 minutes from my sister), but was planning on moving across the country in a few months.

I know my sister really wants me to stay, and a part of that is the pregnancy. Our dad isn’t alive anymore and our mom isn’t particularly considerate. I know she’ll be really helpful when the baby comes, but I’m not sure she’ll be the best support for my sister in the meantime. We have 3 other siblings (32F, 29M, 27M), but none of them are really thoughtful or in a place to be as supportive of my sister as I could be.

I have this whole plan of moving to this new place that I think I would really enjoy. It would let me pursue my hobbies and meet new people. I’ve never really liked where we’re from, and was really looking forward to moving. Now I’m reconsidering as I know how helpful I could be for my sister during her pregnancy, and it would make a pretty huge impact on our relationship in a positive way if I were to stay. There’s nothing really driving me to move except for my own wants. I feel like I should stay to support my sister, because I know I could be really helpful, but it would mean delaying my own goals and happiness for an extra 6 months.

I feel like these decisions are what people remember when you get older. I could choose to stay and build a better relationship with my sister, make her pregnancy easier and make sure she has the support I don’t believe the rest of my family is capable of providing, or I could move away when she’s 4 months pregnant like I was planning and choose to pursue my life as I want. My sister and I haven’t always gotten along, and this feels like something that could really change our dynamic in a positive way, but I would have to make a pretty big sacrifice in terms of my own wants in order to do so.

I haven’t been out of college even a month yet, and I haven’t had any real time to live a life of my own as I wish to. I know exactly where I want to move and what I would do there, and I know it would make me pretty happy. Our home town has always been a bit of a bummer for me, and most of my friends live across the country closer to where I was planning to move to. I thought this year was going to be the first one where I could be selfish and pursue exactly what I wanted, but now I’m not so sure. The idea of putting off my ideal life and independence makes me really sad, but it might be a big mistake I can’t take back if I leave while my sister is mid-pregnancy.

TLDR: My sister just announced her pregnancy and I know I could make her life a lot easier if I stayed in our home city to help instead of moving across the country like I want to. What should I do?