is it cheating if husband kisses another women?

married 20 years husband goes to local bar with male friends 2 times a week meets female they all become bar friends,BUT my husband and her exchange cell numbers they talk everyday (without my knowlege) and kiss once. She thinks hes seperated because she never sees me and he lets her think that.
He says he made mistake cut off friendship told me about it (sort of)
says hes sorry knows it was wrong but doesnt see why I'm making a big deal about it.I almost left him because of this,and he cant understand why.
So whos right?