@Foolish1,
You had an affair with an old flame and he repeatedly told you he was in it for the sex only. He meets your friend, falls for her and she for him and you get upset because she is your friend and shouldn't be bopping the guy who is bopping you (for sex only) because it just isn't right? Do you think maybe is just was not right that you, a married woman, were bopping some other guy? I bet your husband would have a different view about what was right or wrong in this situation.
I'm afraid your friend is right. You have no claim on this guy. You are married and rather than sleeping with this guy you should be working on your own marriage or get out of your marriage had you wanted to be with this guy. I think it is good that you are staying away from this friend and the guy and working on your marriage.
Quote: Recently, I found out that she befriended my co-worker/boss
So, big deal. I don't see how this is a problem for you. Let them be friends.
Quote: Is this even right?
Is what right? That she befriended your coworker/boss? That you are losing your dignity? (Explain how her being your coworker's friend causes you to lose dignity.) Why are you now starting to fall apart? You seem to be getting your life back together. You are working on your marriage, staying away from the guy that you had been sleeping with and whom you had feelings for, taking care of your family and going back to school. Sounds to me you should be congratulated for doing what is best for you. Doesn't sound like you are falling apart.
Anyway, keep doing what you are doing. Worry about what you can control (your marriage, your life) and not so much about the things you cannot control (who your girlfriend is dating, who she is friends with, etc.)