Welcome! You say that you've been happily married for 10 years. I think the proof is in the pudding. Do you think that if your husband wanted to find someone else he would have by this point? My wife had many of the same fears when we first started out. There are two things that are extremely important in this lifestyle. Communication, and time. I agree that you need to find someone else to talk to about things sometimes. I would have loved to have someone poly to bounce ideas off of. Time, you can't do anything about. LOL After being in the lifestyle for as long as we have, we've now realized certain things. Mainly, that we're not going anywhere.
I'm sure there are others on here that have gone through the same experiences that you're having. Use us!! That's what we're here for.
Good luck and keep us posted!