What should I consider first when wanting a divorce or legal separation?

Cheating can be any of a lot of things. It can be a symptom of needs not being met in your marriage, or of loneliness, or many other things. Before you write off a marriage because of this, you need to talk, to deliberate and to let some time pass while you weigh your options and whether you really want out of the marriage or if the other spouse does. Everything in life is a trade-off. What do you gain, what do you lose, are their kids, etc. A divorce is usually better than a bad marriage but a precipitous divorce because someone does something stupid may not be the answer. As to legal separation vs. divorce or dissolution, is there a chance of saving the marriage. How old are you? Are you covered on each other's medical insurance? Are you insurable? Do you want to continue filing joint tax returns. Do you want to write off the marriage and move on with your separate lives? There are lots of considerations other than injured egos.

Once you make the decision you made, step one is to see a lawyer to protect your interests.

What you should consider first is whether you really want to leave your spouse. Then you need to consider how you and he will deal with child custody and visitation. Everything else comes after that.

While I do not practice in your state, I would first say to seek some counseling first to see if you can save your marriage. It may seem insurmountable now, but you may discover later that she made a mistake and may never do it again if given a chance. On the other hand, if you're sure you want out, then I suggest you go straight for a divorce. There's no point to a separation if you're sure you want the divorce. It just costs nearly twice as much and there's not much difference.

Adultery is, of course, a ground that allows you to immediately file for an absolute divorce. However, adultery is difficult to prove, despite whatever evidence that you may have. Moreover, just because someone is at fault, doesn't mean that you should "run to court," because fault is typically seldom given any significant weight in a divorce proceeding. Of course, the specific evidence should be thoroughly reviewed by an attorney who practices family law so that you can have an answer to the question of "what to do first." The only answer that any attorney who replies to your question in this forum can give you is: It depends on the specific facts of your situation and your specific goals.

You have already decided what you want: "OUT OF THIS MARRIAGE". If you have children or joint ownership in real estate, or some other asset, like a pension, you will need to speak with a lawyer.