Is an arbitrator there to make sure that my spouse and I come to an agreement?

No, while that may be a side effect of the arbitration, an arbitrator is there to listen to the arguments and render a decision. He or she is not hired to make sure you both agree on the dispute that is brought forth. An arbitrator may do his or her best to make both sides as happy as possible (much the way many judges in the courtroom does), but in no way is his or her goal to make you both shake hands.