Slowly is the best solution
I have been pondering this for a while, whilst getting familiar with how it works in my primary relationship !
Initially it was a shock to realise that my wife was kind of poly - in so far as she developped a relationship over a number of years without me knowing, so when it all came out, we spent many hours talking about it, deciding it was not an either or choice for our relationship, and then have worked hard to make this work ! She has had no issues with being able to love two people, and now I feel relatively comfortable and secure in our relationship again
This is now virtually "normalised", so after many months of thinking about it, I have begun to feel that to be able to express love to more than one, is a far more natural thing than to be in a traditional relationship and cheating ! Honesty throughout being a key difference to "cheating"
It will be interesting over the coming months to see how it develops, and with the love and support of my wife, or partner as I now think of her, what additional things this brings back into our relationship !
Isn't life just grand !! lol !!