Where do I go from here?

Ok so let me start from the beginning, so that people can make sense of the situation that I currently find myself in:

I have 2 sisters and we were always close when we were growing up. I'm 3 and 5 years older than they are, and when I attended college they still lived at home. They both moved to another city together and have lived there ever since, and when I graduated university they asked me to move out to their city, which I did. We were all close even then, they both got married and had children, and I didn't! I think that's where the issues between me and them began, and have since snowballed over the years.

Whenever the 5 of us (me, my sisters, there husbands) are in the room, they converse amongst themselves and I'm left out in the cold. When I do try to converse with them, they are very short with me, and then they re-direct things back to themselves.

It usually me who makes the effort with them! It's mostly me who texts them to see if they would like to hang out etc, the only time they will text me is if there is some big get together or on holidays, not much else in between.

I am very close with my nieces and nephews however, and when I do hang with them, I never bring my issues with my sister around them. No matter how deep the divide, I would never walk away from my nieces and nephews.

I have texted them about this and they blame me for everything. I told them that I will no longer be contacting them, and if they want me around they can text.