Hello Kathleen,
'to affront' means to treat, mention or speak to rudely. It extends to many kinds of rude treatment, whether verbally or in the form of a certain behavior.
'insult' on the other hand is rather in the form of a verbal remark, that is rude or offensive.
Both actions result in being hurt and offended, while ' affront' reflects a broader sense and takes more forms than 'insult'. 'to affront' refers to deliberate actions of rudeness inclusive verbal remarks,while 'insult' is more focused on such remarks of any kind.
Examples:
"insult"
" His remarks were an insult to their intelligence."
" Their ads are an insult to women."
" affront"
"This incident affronted him in particular."
" He felt affronted when his friend turned his back on him."