<human>: **Background story.**  (throw away was used)  
Mum's sister is Aunty Jenny there is about 17 years age difference. Aunty Jenny married my Uncle John.  
My Uncle John and Aunty Jenny had two children. Uncle John had a thing for my mum when she about 19 and constantly nagged and bugged her about sex and sexual things.  Mum finally slept with him when she was 22, which ended up producing me.  
Mother's family encouraged her to have an abortion and that she should get rid of the child (which is me) mum decided against it and as a result most of the family disowned her.  
Uncle John and Aunty Jenny remained together, having a daughter who is 7 months younger than I am. Then a couple years later another child.  

I found out last year who my father was exactly as I have never meet him and could only sort of remember my cousins. I have a big family, mum has 14 brothers and sisters, so catching up and meeting all of them is rare.  

**Problem**  
Meet my cousin Kelly at a family party, we get along really well, like the same things and lots in common. Her older brothers don't like me as they know the background story regarding me, as does most of the family my age and older. The younger brother and I haven't really talked much.  
As Kelly and I share the same father that would make us half siblings, even though I refer to her us my cousin as that is what we were all brought up with.

I have told her once she is closer to me then she realises but I didn't think it was a good idea to discuss it.

**Question**  
Am I in the right to tell her? Should I tell her? I just have a feeling that she should know.

Give me the gist of the text in a nutshell
<bot>: my uncle who was married in, cheated on my aunty with my mum produced me, half sister doesn't know she is my half sister, what do I do?