I just cant win with this girl what should i do?

I been talking to this girl for six going on seven months i am 20 she twenty five.things have gotten serious I would say but today when I good her lil.brother out.to dinner he was in the back seat like she don't rnt even like him she say he too young and I think it true I feel like she just won't give me a chance but I truly am crazy about this.women I think I'm falling in love I wanna know how should I handle the situation