I plan on refusing to give my sister food even though I offered to get her some.
Why would you lie about this to your sister?
She's the one who is fucking me over! She took my future husband from me!
If you don't feel like sharing, then you don't have to. It's okay to have separate relationships with different relatives, all built on trust.
Fuck that! I'll give her a little and then take some back by not giving her food for a couple days.
It is not bad to not want to share, it is bad that you lied about getting food for your sister. It makes sense that you are upset with your sister if she took your husband from you, just do not stoop down to her level.