I think sometimes you just have to take the love and affection that you get from this world in the form it comes to you...?
You seem to be hesitant to go down this road with this new woman, because it will threaten an imagined possible (monogamous) future... but there's something in you that's brought you this far already
Will it end in tears? I like to think the possibility of that is as high or maybe only slightly higher than if it was a more conventional setup. Why not give the whole thing a try, and if in a while your intuition is still telling you to run, then at least you know you tried