Normally I would suggest telling someone you're poly before meeting up. But this is a bit different. It seems you are interested in more with this woman now and I think I would tell her that that is why you haven't told her before, because you weren't sure. I think I would tell her about your other love in terms of how you weren't sure that it was worth saying anything just yet because its not a primary relationship and you hadn't been wanting to make it so. In this way you are marketing it as something you don't want to lose but also don't want to jepordize your being honest and open either or a relationship with her. If I were her I would find that respectful and flattering.
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