<human>: My (22F) mom (late 50's) just opened up to me about how my dad (late 50's) had been exchanging emails with one of his employees (mid 20's) who is/was also really good friends with my sister. I guess he had been emailing her for about a month after which my mom confronted him and their relationship (she is no longer working with my family). My family chose to keep this all from me until now and I am the last of my 3 siblings to find out since I was away at college and they didn't want to tell me until I came home after graduating. 

This really just came out of the blue for me and I have always thought my parents had a wonderful and healthy relationship (they have been married 28 years) and never expected my father to do anything of this sorts. I just feel betrayed and feel horrible for my mom because I know she has been going through so much this past year and a half with other things in her life. My mom has assured me she doesn't want a divorce and has since forgiven him but wants closure since they haven't really talked about it too much since everything happened. 

Despite this assurance I still feel very weird about it all. I have always been a Daddy's Girl and respected my dad for being a great person/father but now I don't know what to think. Regardless, I just want to vent and want to know if anyone else has been in this situation and if you guys have any advice/words of encouragement.

Could you distill the essence of the text into 1-3 sentences?
<bot>: Dad had emotional affair via email with an employee who happened to be good friends with my sister. I finally found out about it from my mom (4 months later) and feel shitty and betrayed. Any advice?