What complaint does the speaker make about his first wife in lines 13-24 of my last duchess?

He says that she "looked on" everyone, meaning she was consistently flirting with other men, smiling too much, too easily made happy or laughing by men that weren't him. This is mostly summed up in the lines

" She had

A heart-how shall I say?-too soon made glad,

Too easily impressed; she liked whate’er

She looked on, and her looks went everywhere."