Is This Weird?

I'm kinda friends with my ex husbands wife. Like, she's amazing and treats our kids so well. My kids call her mama Tracy. I have no problem with it. Me and my ex are also on good terms. I've talked to her about stuff that stressed me out, she's always happy to help with the kids, and don't you dare call my kids her step kids she will get pissed. I'm happy to share my kids with her. My sister thinks this is so weird. She hates her baby daddy's gf and can't see why we me and my exs wife get along so well.

Edit: To answer a question, no I am not remarried. I have a long term boyfriend. I don't really think I want to get married again. My boyfriend knows that. I don't know how to explain it, just don't want to go through the process of getting married again. I know that's kinda weird. I'm just happy having a partner that I love. I dont feel we need to get the government involved to be happy.