Thanks for the replies and suggestions. Through my company's EAP program, I have set up an appointment with a lawyer.
Of course it was upsetting to discover spouse's extracurricular activities; unfortunately, however, spouse & I were already having problems before my discoveries, mostly due to spouse's non interest in child.
I don't want spouse totally out of child's life. Child adores spouse and when spouse does actively parent, spouse is quite good with child.
At this time, though, given how disinterested spouse has been in parenting child, spouse's lack of resources to provide a stable/secure home, and spouse's plans to either move out of state or in with some unsavory characters (plus spouse's increasingly bad & violent temper), that child would be better off with me initially.
If we have to have a joint arrangement, then so be it. I don't anticipate that spouse will utilize all ordered visitation anyways ... So I am just pre-emptively worrying.
Also, spouse, child, and I have all under gone STD testing. Fortunately everything was negative. We will repeat in 6 months for HIV. Child was conceived through in-vitro, so there are no paternity concerns ... Unless, of course, the clinic mixed up our samples. But child looks exactly like spouse, only with my nose and lips, so I don't think questioning parentage is necessary.
Thanks again.