Cheating?

Husband said I could be intimate with a certain girl friend of mine (on his own not coerced into thinking it) as long as I told him about it. Well, said girl and I made out last night and I told him today as soon as I got the chance. He now feels betrayed. Did I cheat? I feel awful now. I thought it was okay, we'd talked about it months ago and he has teased me whenever her and I have hung out ever since. Saying things like "did you two kiss?" "Has she tried to kiss you yet?" I feel like I messed up and I feel even worse because I really enjoyed kissing her.