I'm sure it's possible for a poly to love and be in a relationship with a mono, but it would take alot more work than if both were poly. The monopartner would have to be okay with you being involved with others... If you are going to try to make it work, stay honest and open.
The first mono I was in love with, I got into the relationship when I was a bit younger and convinced myself I could be happy in a strictly monogamous relationship... I've been keeping alot of feelings to myself and now here I am almost ten years later at the end of this same relationship. If I had stayed true to my beliefs at the beginning, I wouldn't be about to lose someone I really do love. Don't try to change for someone because it will only end up hurting both of you.