I don't know if your wife would find this helpful, but when I was expecting my second child I worried that I couldn't possibly love her as much as the first child. I love her just as much but it hasn't diminished my love for my first child in any way. I don't love one because she is a carbon copy of the other, they are totally different people and I love them both more than I can put into words.
I know exactly what you mean and have a friend who worried endlessly when having her first child that she wouldn't be able to love the child as much as she loved her 2 dogs or that the love for her child would diminish the love she felt for the dogs. In the end, she loves them all (and her second child) immensely.
But - these are descriptions of the point of view of the mother (or the person who has more than one romantic partner). They are not from the point of view of those doing the sharing.
To me, somebody saying that they love me and want to be with me is nice to hear but without action, it's meaningless.
I grew up as the oldest of 3 children and I hated having siblings. My younger brother was a demanding baby and child and I was left to my own devices lots of the time. As teenagers, my sister had needs that took up lots of our parents time and attention. I grew up feeling abandoned and never good enough. If I'd been able to care for myself, I would have left my family - and as I grew older I did spend as much time as I possibly could away from them.
As an adult, I love them all. I'm very happy to have my siblings and my mum and we've helped each other through some really tough times. But my relationship with my mum has been seriously damaged through nobody's fault really. Mum loves me loads and it isn't her fault that my siblings needed more from her than I did. She coped the best she could under the circumstances.
I think that a more useful thing for the OP to answer is how does he plan to set things up so that both his partners feel loved? How much time and energy do each of them need and can he meet that? If not, would it be better to take his wife up on her offer to leave? He's not the only man in the world and she could, I'm sure, have a relationship with somebody else who had the time and the energy to be with her in a way that she would like.
Feelings of love are simply not enough to make relationships work. Time and energy are just as - if not more so - important.
IP