If you want to keep discussing this I would suggest you start up a thread under 'new to poly' . It is an interesting topic :-) It's a lot of work for the mods to have to shift threads out of here that take off beyond and introduction.
In answer to your question "Why shouldn't you explore until you're ready for him to have the same opportunity?"
1. I don't believe we should ever ask something of another that we do not also expect from ourselves.
2. Poly works best when existing relationships are really healthy. The healthier the better because if there is any dis-ease you can bet poly will not make it better it will highlight it.
3. Your husband might be fine with it intellectually but emotionally is another issue.
4. The people you explore with are people too, with emotions. I don't believe it's right to explore with other people's feelings until you are very, very secure in your own and your husbands.