Merging of two email accounts

I somehow combined my personal email account with my work.  All my information and contacts/FB are showing in the business email.  How do I undo this.  When I open the business email my microsoft login automatically pops up.  I deleted all the business contacts from my personal email and it deleted them all from the business email.  I can not get rid of all the FB contacts.  I want to undo this. Please help !