I have to echo what redpepper said - just because you are a sub doesn't give anyone the right to violate your own boundaries.
Based on what you have said, you set out boundaries for opening your marriage and he rode rough-shod over them because of his impatience to "get on with it". He betrayed your trust and showed you little to no respect.
I agree that right now you shouldn't be concerning yourself with anyone else outside of your marriage - find out whether you can get back to a feeling of stability and trust with your current partner. I strongly believe that a relationship has to have solid trust as a foundation and that an open relationship needs it even more. It doesn't sound like you have that right now, and that is what you need to find out whether you can get back or not - and that is between you are your partner.
A question - now that you have realised what was going on, and have presumably explained it to him, how does he feel about this?
"Listen, or your tongue will make you deaf." - Native American Proverb