You guys have a very limited perspective. So one part of your health may have slightly negative effects from monogamy. What about mental health? I can't imagine that sneaking around in this day in age of cellphones and internet is that easy. How stressful would that be? What about the stress of family discord? It may be a trade off, but you should consider which is more important to you before doing anything stupid.
Also, this whole idea that we can't be something because we weren't biologically programmed is just silly. We're not talking about slugs or dogs or even apes. We're talking about humans with the most complex sexual organ on earth...the brain. Plus, humans do shit all the time that we weren't naturally supposed to do: Break sound barriers, defy gravity, submerse ourselves in water for hours at a time. All such complexity derived solely from that magnificent mind of ours. Why should human relationships be any less complex?