Jealousy is not rational. The stuff that makes us hot can also make us jealous. He's giving you mixed signals, and I know how confusing that feels (been there years ago with my husband, with a slightly different situation). He has a hard time telling you what he feels and what he wants because he probably has very mixed feelings about it himself.
At the time, I chose to stop everything with the person I was seeing, because the emotional turmoil was too much. With time, the boundaries became clearer, and communicating was much easier when there weren't so many emotions at play. However, I wasn't in love with the person I stopped seeing, and wasn't expecting anything to come out of it, and I didn't have a resource like this at the time: thus, my marriage was by far my first priority, and I wouldn't have been able to do the required communication and balancing at the time even if I had had the motivation to. After I stopped seeing the person, me and my husband both took time, we let the open relationship issue be unresolved for some months. With time, both of us got some perspective, feelings we had became less intense, we were able to understand ourselves and each other better, and were able to communicate clearer boundaries. After that there haven't been these kind of problems, and we are now happily poly.
Only you can decide these things to yourself. Your communication with your husband might be easier if you take a time out from the open relationship, or even if you just slow things down. You should assess yourself, how important the new interest is to you, since obviously he may not wait around for you and your husband to work on your marriage, particularly if you can't give him any timeline. And you can try to work things out as they are: it isn't impossible in all situations, and only you can know if it can work in yours. What's for sure, it will be more difficult.
Last edited by rory; 11-14-2011 at 12:50 PM.