SG has some good points. I wonder if your partner now knows about this other man that you talk to. I think starting with that is the best bet and then take it slowly. You could tell him the story of how you met and what you talk about. What it was like to meet him, it you have, how hurt he is that his last relationship ended not long ago, how you feel some love for him and want to be there for him... that would be a good start. Let that settle and then add to it in little bits by telling him what you and him talk about. Engaging him in your friendship I think is the best likely scenario for success.
As for not wanting to share, well, you can't predict what will happen. If you want an open relationship then you can request all you want that they not fall in love and want to be together to, but really, when it comes down to it, you have no control over that and could very well have to let that go.
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