You are already married. To your wife.
You can't have 2 marriages.
Does your State allow same sex marriages?
Even if you could/did marry .. you would still be cheating your wives. It would not matter how secret you make it, you would still be cheating your wives. This is crazy, but if you have one woman partner, and one man partner, in marriage - you would always be cheating on one of them.
Your wives, should be given the choice about both of you.
They should be given the knowledge that their husband is having an affair with another man .. and do they wish to accept that? It is their decision. However, the wives should definetly know about this, and be given the choice to decide.
One day, your discreet & safe secret, may be made know to everyone .. including your wife, and your children. And it could happen at a time that you are completely unaware.
Your wives need to have a choice.
This is your decision. The decisions you put in your life, determines your life.