Hi. I am also really new to this board and trying to accept myself as a poly person. What I can tell you is that the one time I did try a poly relationship (myself, my husband, and my girlfriend), I felt LESS alone than I ever had in my life. I too was afraid of losing that one-on-one connection (with my husband). But, as it turned out, we gained so much more. This other partner, whom you say you have love for, is not a competitor, but another ally. The more people we love, who love us and accept us, the less alone we truly are.
Good luck to you and I hope you find all the love and happiness you are searching for.