The primary reason we don't investigate infidelity cases is because, based on our experience in Washington, it doesn't help you much in court.
Now please don't take legal advice from us (or any private investigator). Ask your family law lawyer or LLLT, "hey will hard proof of my partner's infidelity help in terms of spousal support or child support?"
In our experience the answer is generally no. And as a result we don't feel good about taking your money to provide a service that generally isn't useful in court. We think that money is probably better spent on couples therapy, attorney fees, or a deposit on a new place to live.
We recognize some people "just want to know" or "just want closure" and there are many other private investigators in Washington who will help you with this type of work. You are welcome to contact us and ask for a referral to some PIs who do. It's just not a service we feel good about providing, so we don't.
So before investing thousands of dollars in surveillance of your partner, please check with your attorney or LLLT and ask them if it makes sense for your case.