Some of these responses are quite brutal and a bit unfair!
Op, It sounds as if your sister has good reason to distance herself from your parents/the old family unit. I do agree with others there.
But your problem in feeling hurt by her actions is different - you are allowed to feel the way you do and your feelings are valid. This doesn't mean that her actions are necessarily wrong, but you're entitled to feel hurt by them.
You don't elaborate much on your personal relationship with your sister, but you seem to have a level of bitterness about her absence. This is usual where one siblings does the legwork with family members who need a lot of support.
It sounds like you're struggling a lot and perhaps you're looking for support from your sister that you're not getting. Have you ever asked for her help?
Equally, if she knows that you feel resentful this will likely push her away so may account for her distance. It's really difficult in adult families to balance the needs of each other, individuals aren't necessarily at fault but it can be incredible complicated and difficult to communicate openly without emotions flaring and causing divisions.
I think you need to try and break down to yourself just what you're upset about as a starting point.
Is it that you wish you had a closer friendship with your sister or is that you wish you had more support in looking after your parents? Or both?
What were your respective roles in the family growing up? Often we carry these through to adulthood.
I agree speaking to a counsellor would be helpful in working through how you feel and to help you find a non-confrontational way to speak with your sister to improve things. Or just to learn to accept the distance and move on.