I've been there with my daughter and it has broken my heart when she was let-down or hurt by her mother's drunkeness or absenses, or when she has had to spend many hours alone. I'm never sure what is right in this situation other than you must teach your son that his father is 100 percent responsible for his own actions.
Per the drinking on the weekends, if you feel your son is in danger I highly recommend consulting a lawyer. If not, let it be and get to an Al-Anon meeting ASAP.
Per the transportation I don't know if this helps, but my daughter has been taking the bus by herself since the age of 11. She also walks a lot (farther than I ever imagined when I was her taxi driver). Neither my wife or I drive her unless we can do so conveniently. It turns out she is capable of many things when we leave her alone to do them, and give her permission to do so. ;-)
Per what your ex thinks about you, it doesn't matter. You know what you know and you know it.
Originally Posted by
jackthedog 
So what do I do so that my son can see his father without me always driving him? I do agree, but at this point my EXAH thinks I am nuts to think that he is an alcoholic. How do I stop him on the weekends when he stays with him? I am so open to ideas.......thanks.