Should I stay quiet

Recently my fiancé’s ex brothernlaw passed away this is the mother of his child’s brother they have never been married only a really weird relationship apparently he got her pregnant while she lived with him and his then wife this happened years before my time. They are no longer together but she hates me hates for her kids to be around me I love them and they always go home and say how much fun we have together. But that lady hates the air I breath she says the only reason why he wants me is because I’m lighter and my butt is bigger 🙄 I know shallow anyway I have no hard feelings against her but she is really needing him a lot since her brothers passing. It’s getting to the point she’s calling everyday for him to come over because she can’t stop crying and it’s making me feel some kinda of way should I tell him or would that seem selfish of me???