I'm guessing your ex is failry young still?
Remember noone knows how to be a perfect parent, we all have to learn and learn from our mistakes and get help from our mother, health vistor, books, or whoever will listen!
Perhaps suggest he should consider going on a parenting course to help him learn some of the basics as he's not seeing much of his son, and not very hands on. It must be hard for him when he feels he is doing the right thing seeing his son, only to be yelled at and criticised for it. Ok most people would agree that taking a baby to the pub to watch football isn't quality time. But at 8 months your son might well have fallen asleep on the walk, and the pub is smoke free now remember. He probably got a fuss made over him too, and all the chatter and noise would have kept him entertained. I doubt he was in any danger being in a pub, so how can you justify cancelling all contact unless supervised.
Maybe instead of yelling at your ex, try and stay calm, make it clear you don't approve of the pub and suggest he leaves taking your son to the pub until he is old enough to appreciate it. And then suggest places he could take him instead, like to the park or for a walk around the shops, to the library, feeding the ducks/pigeons or wherever you think. Why not try and enroll his mum or sister to visit with him so if he takes your son out they go with them. You might end up with him taking him to the pub and just not telling you if you yell at him for it.
Also you might well see cancelling friday and saturday while you waited in all day as being unreliable, but he might feel that he is a free spirit, you are not together and he had (in his eyes) good reasons not to be there and managed to get there as soon as he could, which was only sunday after all and what's the big deal...
Next time text him if he doesn't arrive at the appointed time asking if he has been held up and that you will wait in for another 15 minutes unless you hear otherwise from him. And then go out, for a walk, for the rest of the day, to the library, a friends, wherever. But don't be sitting at home waiting for him. If he then turns up and you're not there maybe he'll think twice about letting you know if he's runnign late next time.
I don't think there is a magic wand you can wave to make him realise what a responsibility it is to be a parent, and that even if you son is only 8 months old he needs relaibility, consistancy and a father who is part of his life and committed to his child. But encouragement and help might work better and help build his confidence so he wants to be around his son more. Then again it might not. I'm just saying try and see both sides and find a solution. Not easy i know, you'd probably still be together if you could work things out and compromise. Stay strong, stay calm for your son.
Put the parenting course to him, he may not even know about them.
Deep breathes, he's not worth your anger.
Gilly