You can use mediation whether or not you are married and whether or not you have children.
You can use mediation to help you devide whether your relationship is over. If you decide it is not, then you and your partner may want to seek counselling.
Mediation is always voluntary. However, for mediation to work, both you and your partner both need to take part, and neither of you should feel threatened or pressured by the other. It is also important that you are prepared to share information about your situation with each other.
Mediators do not act for just you or your partner. They are trained to act impartially (without taking sides).