Welcome! My advice, since you asked, is to start very slowly. before you introduce anyone else, work some stuff out for yourselves.
First understand your own needs/wants and likes for the relationship, then compare notes with your partner. Come up with boundaries that you are not willing to cross. You may knot have the answers to these before you start doing it, but the more you do know about the other, the better.
Typical things to ask are:
* Are you going to always date as a couple, or is it ok if one of you goes out on a date with the person
* Is it ok if only one of you has sex with this new person, or must it be you both together?
* Is it ok if the other person is already in a relationship? It is ok if, while dating you, the person has other relationships?
* Is it ok if the person has children?
* Are you expecting that the other person would eventually live with you?
* If the person has another place, is it ok if one of you sleeps overnight there?
So much of the next few questions will depend on those answers. If you want to use this board as a sounding board for them, please feel free - a lot of us have been through this sort of thing, but everyone is different.
Please check out The Birdcage - an open, friendly Polyamory forum for all parts of New York State
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