NRE and Primary Relationships.
It sounds like your husband is expressing some real concerns (and possibly fears) there. It can be challenging to really understand and have compassion for a reluctant partner when you aren't standing in their shoes. You love him, and share a life with him; you also have strong feelings for, and share a real connection with your lover. Holding all that love in your heart is a wonderful thing, and it can feel strange or confusing to not have your partner be as excited about it as you are.
Purely from my perspective, I think that when you come up against someone else's limitations or fears, that it's important to take some time/space from a secondary relationship and really address them. While you feel love for your new partner, it's a different connection than the one that you share with your husband, and it might be more important that you think it is to make sure that your husband knows that. I'm talking date nights, great sex, romance and fun - let that NRE spill back into your relationship with your husband and strengthen that connection. Find out what he needs to feel great about your new relationship; process, communicate, talk, fight, txt, chat, drive around with coffees and process some more. The more you invest in making sure your primary relationship is in a great place the healthier it will be.
NRE is a tricky one to navigate, and it's super important to take care of our primary partnerships and other relationships in the midst of it. When I've been the hinge in a vee before I try to remember that I'm having a TON of fun, and that it's really important that I'm sensitive and gracious about that experience.
I think it's awesome that you've found two people to love, and that you're looking for ways to make sure that you are doing what you need to keep your relationships healthy. Keep reading, posting and communicating!!