The abuser can also be anyone, but we can distinguish that they are: 
- coworkers
- coaches
- teachers
- patents
- spouses
- boyfriend or girlfriend
- school mates
- children
- care givers
- family members
Unfortunately, the abuser is usually someone the abused person knows, relies on, or is very close to and trusts.
http://mypolice.qld.gov.au/farnorth/files/2013/05/emotional-abuse.jpg