Hello MorningTwilight. I was in a similar situation as you, except for the fact that I was deciding to tell my boyfriend of 2 years. Not twenty. He and I shared a home, finances, responsibilities, you name it. We were also very in love. And I was also falling for another man.
I made the decision to tell him how I felt, I planned ahead of time what day to tell him, and when it finally came, that moment I knew I had to say something was possibly one of the scariest, most heart-stopping, shaking in my boots, pale faced terror-gripped moments in my life thus far.
But it started with the hard decision that I needed to do it. I felt agonizing guilt for half a year prior, knowing that I had feelings for another person. I never stepped a toe out of line when it came to our expectations of monogamy, except that I had these feelings I couldn't express that were slowly eating away at my happiness. After a long time I decided that I didn't care if it was insane, that I would learn to love two people, and that had to be acceptable somehow.
Think of as many different outcomes that may come as a result of you telling your wife how you feel. She may leave you outright, she may decide to work on it with you and take many years to feel secure enough to venture into an open relationship, she may tell you there's actually a guy she's been wanting to date too, she may flat out say no, she may say yes.
If any one of these possible scenarios is too unbearable or not worth the prospect of living a polyamorous lifestyle, then don't do it. But if you can imagine the worst case scenario, say she decides to just up and leave you for even suggesting this, and can imagine saying to yourself "Maybe this had to happen. I would not be happy if I continued to remain monogamous, and in turn our marriage would not have been happy" Then perhaps it is worth the risk.
How do you feel when you consider staying monogamous for the rest of your marriage? Which is worse, the prospect of staying monogamous with her for the rest of your lives, or her leaving and you both continuing with your lives separately?
It sounds kind of macabre to think of it this way, but these are important determinations before you can resolve to do this. Its that resolution that is the first step to making this a well-thought out decision, and opening up polyamory to become a part of your reality.
For the record, I did tell my boyfriend. We were both terrified of what this meant, but when he saw how frightened it made me to think of losing him, he kind of understood that this wasn't about just messing around, or trying on another guy before I decided to dump him. I made it very clear that I was being honest, and that I loved him as much as ever, and I intended to keep him in my life. This was not about replacing him, it was about wanting to not have to lie and go behind his back to feel fulfilled and feel love with others.
It took constant reassurance, and constant communication, but we did open up our relationship. Our 4 year anniversary is in a couple weeks. <3 We're as happy as ever.