You know what would be a cool thing to do? Call the house number of the girl until her husband picks up and say something along the lines of "Have you seen my boyfriend around your house? He's been meeting up frequently with your wife who happens to be his ex, but I need to tell him something". And then see what happens
What he's doing is abnormal and I think you need to confront him on this. Maybe confrontation will exacerbate the situation and maybe there will be a drastic reaction. But can you seriously continue living like this, knowing that it's getting worse and worse with each passing day?
Tell him, plain and simple. Show him the bill, calling an ex everyday is not normal and you will not stand for this. Don't let him treat you like a doormat.
Don't cry, don't regret and don't blame
Weak find the whip, willing find freedom
Towards the sun, carry your name
In warm hands you are given
Ask the wind for the way
Uncertainty's gone, your path will unravel
Accept all as it is and do not blame
God or the Devil
~Born to Live - Mavrik~