"To get worked up" mean to be excited and agitated but in a negative aspect. So, if someone is worked up about a person, they are over emotional and agitated over that person and don't stop think about that person (but not in a good way, in a "it's annoying" kind of way) I hope this makes some sense :p

Don't let something anger you. Also, you can say "don't let it get to you"

"emotionally excited and especially angry or upset." http://www.merriam-webster.com/dictionary/worked%20up