Mono/poly dynamics are a hot topic on this forum... try doing a tag search and see. There are a lot of people that come here to get some insight on how to make it work. It isn't easy but it is doable.
First of all there is no reason why you can't have other lovers and your husband not. It will take huge responsibility to manage your time. Especially with kids involved. It would take a huge amount of his ability and desire to let go of you being around all the time and he starting in on some of his own projects and life goals by himself. That could be a good thing for him... I know it has been for my husband since I started dating Mono, Derby and Leo. He has taken his life into his own hands and made some significant life changing alterations as a result. He is far happier for doing so.
There is not going to be a way to convince your husband that you should be poly. Someone will always draw the shorter stick on this one. That is just how it is. There will always be compromises, and you likely will find it hard to find any way to reach and agreement on boundaries, but you can keep at it and keep trying. I have for almost three years. I have found a way that is good for me right now. Maybe you might also...
If I were you I would keep being patient. I can tell you one thing that I have noted for sure... rushing and letting your desire get ahead of you will set you back big time... maybe you already know that since you have cheated once already. I would keep breathing, think of your kids first and note that life changes in its own sweet time.
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