Thank you Anneintherain!
Yes I do very much think this is an issue of not having as many close friends. I have always been a shy introvert, though I have been trying to take steps to change that. Also, though we have been dating for over a year, it was 4 weeks ago that I found out he texts them every day. Before that, I treasured the texts he sent me every day, because they made me feel special. Now, I am just one of many. I know this is petty, and I don't want to feel this way, because he has told me time and again that the emotional connection with me is so much greater than with them. I just wish I had more self esteem, so I would believe that! I mean what more does he have to do for me to believe him? But I just can't find the key to release the fear.
I know in poly, self esteem is imperative to help you through jealousy, and I have been working very hard on that. But I still have a long way to go and it is a very slow process.
Thank you for the book suggestion. I will check it out.