I'm going to vent to my friend about another friend only to have her tell him what I said
What is the reason you want to play gossip telephone?
I was fed up with him and I wanted him to get his act together.
It is normal to vent with your friends, it is good to let those feelings out but you shouldn't do it with the intention that they let another person know. It will hurt his feelings and hurt your relationship.
It's no big deal, I'm over it
I think it is good you have support but it might be hurtful to tell someone your relationship woes. If they say something they could spread some rumors that you will regret later.