That depends on what you mean by “nice”.
Do you mean “with kindness”? Not necessarily kindness, but certainly decency. You are morally obligated to treat your spouse with decency, but you don’t have to go out of your way to make the spouse you are divorcing happy. You don’t have to capitulate to your spouse’s unfair or unreasonable demands.
Do you mean “with honesty and fairness”? If so, then yes: you are morally obligated to be honest and fair with everyone, but again aren’t obligated to capitulate to your spouse’s unfair or unreasonable demands, nor are you in any way obligated to tolerate being treated unfairly by your spouse.
Do you mean “forgiving”? If so, then yes: you are morally obligated to forgive your spouse for the wrong’s he/she did you, but forgiveness does not mean “acceptance”. Forgiving the people who have deceived or betrayed me in the past does not require me to trust them in the future. I forgive them so that I don’t dwell on the hurt done to me, so that I don’t let the injury continue to harm me, so that the one who did me wrong is shown the mercy needed to give him/her the best opportunity to change for the better without eternal regret or shame hampering the repentance process.
Fighting fire with fire will only intensify the pain and misery. Being the better man (or woman, as the case may be), living up to your virtuous values and standards of conduct is the only way to move on with peace and happiness (and you can get back there). Easier said than done, yes, but the only way.
Utah Family Law, LC | divorceutah.com | 801-466-9277
https://www.quora.com/Should-I-be-nice-to-my-spouse-during-a-divorce/answer/Eric-Johnson-311