I believe, Plato was advocating for objective view of beauty.

Say, this girl I am madly in love with. Suppose if she is to start gaining weight or fall ill and lose her appeal.

Would I continue to love her? When I think deeply about it. Truth is, I find her beautiful because how see looks to me now.

However, when I start imagining, her gaining 20-30lb. I find myself asking, she is cute, but she is short and on curvy side. The thought itself frightening.

According to Plato, if I really, deeply love her. My love should not change with time. Because I find her beautiful not based on my feeling or how she appeals to me now.

He is saying that I should find her beautiful based on reasoning rather feel or look.

isn't that what we all want from someone we love. To love us for who we are.

I agree. However, suppose I am asked to convince bunch of people that Plato was correct in saying that Form of Beauty is reflected in all beautiful things. What could be few examples.

I am trying to understand thinking behind Plato's reasoning.