First....breathe. Honestly, I think for the time being, you need to keep your marriage closed. If you don't, every single time your husband meets someone or dates someone, it will chip away and drive you batty.
You don't like being caged in, but you aren't ready for a full-blown polyamorous relationship. Slow it down and focus on your marriage. If you're going to continue, you need to place boundaries. (E.g. Every night I expect you to sleep next to me. I expect you to not neglect me or our marriage. I expect equal attention despite NRE. Within the walls of our home, we're only talking about our relationship because I don't need to know about you and her or whatever. So on and so forth.) He has to make you feel comfortable. A huge part of poly is compersion. If you're insanely jealous, questioning whether or not you're good enough, and not happy for your husband...that's not the healthy side.
You have self-esteem issues, and you need to work on those and be happy with yourself and not rely on anyone to make and permanently keep you happy. I know that with or without my husband and our girlfriend, I'll be happy and be able to stand on my own two feet. You're also lacking confidence. Men love a confident woman. Confidence personifies sexiness. Be confident in the fact that though some other woman may be a lover or girlfriend, you're still his wife. Any man or woman that can be taken was never really yours from the beginning.
An integral part of marriage is having interests and friends outside of your spouse. Find something to do while he's out. Maybe you can date someone. When my hubby is out with our girlfriend, I spend time with our kids or I have a ladies night where can kick back, laugh, and act like we're at university again. I also pamper myself. I'll go to the spa or Agent Provocateur. I'll buy lingerie in his favourite colour and make him do a double take. I don't know everything about their relationship. She doesn't know everything about our marriage either.
Does your husband make you feel sexy, loved, and wanted? I mean before polyamory entered the marriage. You will always be his primary, the first, and the only Mrs. Nobody can take that from you. He saw something in you that he saw in no other woman that made him say, "I want this woman to be my wife and the mother of my children." You have to keep the spice in your marriage and not let outside influences take away from that.
With polyamory and all relationships, you have to communicate. Tell him how you're feeling and be honest. If he loves you, he'll reassure you that he's not going anywhere.
Not all poly people are slutty and not all men want a bunch of notches on their bedpost. Prior to this year, I was the only woman my husband had been intimate with in our almost 11 year marriage. I, on the other hand, have had the same girlfriend since '00. Outside of him, that was the only other person. Now, my girlfriend is our girlfriend, and our triad is closed. I suggest reading the book Ethical Slut. I had to read it for a class during university. I forgot the author's name.
Fear is normal. It's the fear of new territory, the fear of being replaceable, the fear of opening your heart to someone new, the fear of being judged, and all these things are normal. Just relax and keep working on your list. We're all here for you, and we've been where you are. Good luck!
Ry - Me. Panromantic demisexual with a history of polyamorist tendencies. Married to...
Mr. Grey - The once distant stranger that I complement beautifully. DH of 12 years and father of our (3) children.