can you lose custody of child or children if you are an unfaithful spouse in the usa?

This is your 875th answer, Enrique.  Child custody awards are based upon what is in the best interests of the children. But any lawyer would probably advise you to avoid affairs until the custody is settled. (I do know of one situation where this was the case.) You should consult a family law attorney, do not rely upon advice from amateurs, here. Good luck.  

It's not a consideration in custody disputes.. During my divorce settlement hearing, the ex accused me of having a live-in GF.  The judge said that was a point in my favor, because I would have help caring for the kids. I got custody.

I see a lot of divorces, and the ONLY time I've seen a woman lose custody was because she put her child in a dangerous situation when she had an affair.

Probably depends on the law in each state.

No, not unless you also abandon the children or neglect their welfare. Being an unfaithful partner doesn't always equate to being a bad parent.

No, not at all.  In the United States, custody of children goes to the parent with the vagina.  It doesn't matter if the husband is unfaithful, as the husband doesn't have a vagina.  (he's not getting custody)

It doesn't matter if the mother is unfaithful, as she does have the vagina (she's getting custody)

No.  Most wives in the United States are unfaithful.  

Yes, but not for the infidelity. You get divorced and it's more than possible that you can lose custody.