now what

my husband and i had a conversation/situation this past week.  I found him sending an IM to someone asking them to get a hold of him, a girl, well, long story short, it shouldn't matter because our relationship is not going to last, so why am I getting upset over it was answer.  He said while we are married he isnt doing anything that is harmful to our marriage...he is right, what does it matter, he is leaving me any way (has been leaving me for the past i dont know how many years) I need to just get the balls to leave already.  I dont, i hang around like an annoying fly.  It sickens me that i am wasting so much time in this back and forth nonsense.  why do i do this to my self.  I want to be married, i want a family all that wonderful stuff, but i dont want that now, i dont even have the ground work for that now so why on earth am i affraid to leave, being alone wont even be harmful,  I need to grow balls!!!!!!!!!!!!!!!!!! ugh.