Sorry, but the first thing that screams out at me with your post Nevins, is safety!!! Your wife thought your best friend was the father. This makes me wonder, were they protected? Tested? She wants to reopen the relationship now that she can go back on birth control. Unprotected?
Just be careful...
In my 20s, before I even knew there was something called polyamory let alone that this could be me, I would find avenues for my sexuality in similar ways to what you're describing. It never felt good because it lacked the openness and maturity that my poly relationships have now. It felt shallow.
This may not be your experience, in which case, go forth and do whatever fancies you. My experience has been that a solid base in honesty goes a long way! If you're worried about jealousy when it comes to your wife having feelings, I'd suggest the best thing is a lot of conversation. Also, an agreement within which you both feel safe. (ie: you are allowed to interrupt your wife and her lover if you start not being able to handle it).
My heart is too big to fit into one person.