In Act 3 Scene 2 Bassanio has to choose the right chest or lose Portia. He is struggling to pick the right chest. His love for Portia is real, and he can't imagine living without her. Bassanio has a unique way of defining beauty and what beauty isn't.
He tells us that beauty should not be judged by the outside appearance of someone. He says that outward beauty can be bought, but what is on the inside will eventually come out. If a person is not beautiful on the inside, then all the jewels and make-up can't cover up the true reality of what that person really is. Bassanio thinks that Portia is beautiful on the inside as well as the outside. Her true beauty shines through to what he sees on the outside. He has harsh words for people who try to disguise their ugliness with what is considered beauty.
"So many outward shows be least themselves: The world is still deceived with ornament. In law, what plea so tainted and corrupt, but, being seasoned with a gracious voice, obscures the show of evil? In religion, what damned error, but some sober brow will bless it and approve it with a text, hiding the grossness with fair ornament? There is no vice so simple but assumes some mark of virtue on his outward parts: How many cowards, whose hearts are all as false as stairs of sand, wear yet upon their chins the beards of Hercules and frowning Mars: Who inward search'd, have livers white as milk."
We see that Bassanio has contempt for people who are fake. There are people who hide the true ugliness inside their hearts with the outward appearances of beauty. Bassanio defines beauty as being the beauty on the inside, like Portia. Her beauty comes from within. When Bassanio looks at her, he sees the beautiful heart and spirit she has and that is what made him fall in love with her.