I know what you are talking about in terms of worrying about doing some harm to the happiness you are feeling now. I was so scared when I pondered over the possibility to start the 'poly-journey' to lose what I got before everything started: love and happiness with my husband. It took me almost three years to wrap my mind around poly. If you are interested, part of my initial struggle is noted in my blog on this side (see signature).
I wouldn't call it closed minded, I just need to know what the downside of things could be. And I need to think about them to feel save to face them. And there are many
possible downsides to poly, if you read a bit of the stories that have been told here, you will find plenty. I can't throw myself into things without having them meticulously sorted out.
Fear can be something quite healthy, as long as it helps you process things in a way that make you feel secure and save at last. Listen to your fears as long as they don't paralyze you completely.
Facts: 30, female, bi, v-type relationship with Sward (husband, straight, mono) and Lin (boyfriend, straight, mono), poly-fi and co-primary.