Recently it seems like open relationships, open marriages, and polyamory are more normal than not, so please know that you are not alone in this desire.
I think it is important to do some self reflection before anything else. I'm sure you have been but it must be said. Do you actually want to be with both of these people? Or are you falling in love with someone new and don't want to let go of your past? What are you open to? Will you be able to give your husband the same support? How would you respond to him asking you the same question? What if the idea of a threesome comes up? Are you looking for a distraction or escape?
I fully believe that open relationships can work. They can be happy, healthy, and fulfilling as long as there is absolute honesty between partners. I have never been in an open relationship but I have dated people at the same time and that got messy, real quick. Mostly because I was being an ass but that is a story for another day.
After you've realized your feelings on the matter, take time to think about the things you value in your current partner. I think bringing up the idea of dating another person usually brings up insecurities, "am I not enough?" "are you not attracted to me anymore?" "am I boring?" so many negative thoughts can come from expressing that you have feelings for another person so take the time to be ready and fully able to express how much you love and care for your husband. Make it extremely clear that you're not looking for a replacement, you're looking to explore new feelings and want to include him in that.
Maybe start the conversation more causally, bringing up the idea of an open relationship in general, not "I have feelings for this other person". Explore questions similar to these...and be HONEST with yourself and each other
Would he be open to you dating another person completely separate from him?
Are you open to him dating someone else?
What boundaries would need to be in place?
Would your separate relationship be talked about with your husband?
Are they places and spaces that are off limits? Dates?
Is this other person welcome in your shared home? Your shower? Your bed?
There are so many ways to unintentionally hurt your partner when bringing someone else into the picture. It is true that you don't know what you don't know so you'll never be able to make a full list of "rules" but being ready with guidelines and also ready to say "I don't like XYZ..." immediately will keep resentment from growing and hopefully bring you closer.
Most importantly remember that this is YOUR relationship. No one else's. What works for you and your husband is what you should focus on. Don't worry about labels, maybe you don't stay open forever, maybe you do. You don't have to know these things now. There is no checklist of what is required to do this successfully, other than of course honest (and KIND) communication.
Okay, secondly...does this woman know your feelings?? Have y'all already discussed any of this? Does she want to be with someone who is married? Has she met your husband? What happens if he does say all is well, y'all date, and then... is she allowed to date someone else? Marry someone else?
Maybe this has just created more questions for you but I think if you are honest with yourself, your husband, and this woman, you'll be just fine.
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As always, love you all. Kiss Kiss.