How do u tell someone you don’t like them

Seriously how? I have or had a great relationship with my brother, him and my husband are/were really close. It’s gotten bumpy because of different situations or opinions, but anyways I used to get along with his gf but 5 years later I’m starting to see her real colors. She literally rejected his proposal for marriage, doesn’t want to have kids with him. Nothing ..... they are just together as gf and bf. I’m not saying I want her to marry my brother by force but just with our culture we get married and maybe start a family if you want but at least married if it’s the right person. He’s the only boy and youngest, & all my sisters are married with kids myself included. I know my brother he’s always said he couldn’t wait for marriage or to have a family and now he rejects the idea of it! I feel like she changed him. She’s making him be more like her and he’s so in love he can’t see how she changed him! And she’s been in the family for about 5/6 years and acts so stuck up with my family she barely says hi or greets my parents when she visits! I can’t stand her! My problem is we used to hang out a lot as couples but I don’t like her and my brother is always trying to hang out or come to my house! I always make excuses but I just can’t anymore! How do I tell him I can’t continue this relationship with them! I don’t want to lose my brother or our relationship but I can’t keep faking this 😢 I’m honestly broken