To say that it's not possible to have a relationship over the Internet or that there is no relationship here...four months and not meeting....This is not the issue.
The issue is that after 4 months of this relationship...online, LDR...whatever it may be, two people are sharing their feelings with each other and their trust their love and commitment.
She has cheated on you. Are you willing to forgive her?...
If she wanted to be poly she should of spoken to you before any of this happened. It's difficult with LDR and online...You need Alot of trust! Can you re-build it after she has cheated on you? and are you ok with this sharing idea?
If you dont agree to be poly...will she be with this male without you knowing?...Even if she says she is not with him anymore...will you believe her?
There are many things i think you need ot ask yourself and think about. You need to talk to her for sure!
If someone i trusted cheated on me....I'd walk, there is no excuse that makes something like this ok.
If you're poly you tell your partners you talk before you take action!....sometimes it takes hours...days...weeks...Years! But if you love someone and care for them you're willing to take the time.
To stay in this relationship...you're not only saying "What you did is fine hunny, You can have free range of people you like....sleep with whom ever" You're also rewarding what she did!
Don't lust for what you want, desire what you know