Desperate.

VictorM's advice:

Yes, it is hard to change.

That type of behavior is as difficult to change as it is to change temper, sense of humor, mood swings, confidence, self-esteem, shyness, procrastination, etc. Don't make light of how difficult these changes are, and you can't expect people to change just because something seems so easy to you.

Start by accepting that his "unreliability" is a product of his upbringing and personal experiences, not a reflection of his feelings or respect for you. In essence, he was this way before you came along, and he'll be this way if you leave, unless he seeks professional help to get to the bottom of why he is this way and what he needs to do to change.

Meanwhile, how can you deal with it, if you so choose?

Cut down or loosen up his obligations and reward him for good behavior. For example, if he was suppose to call you by 2 o'clock and at 3 o'clock he remembers, he's likely not to call at all because he knows he's already in the doghouse. He'll postpone being yelled at as much as he can instead of calling as soon as when he realizes it.

If calling you by a certain time is not important, don't give him a time frame. If you give him fewer opportunities to screw up, he'll screw up less.

And next time he calls you late, instead of telling him off, just say you're happy he called and act nicely. This behavior from you is more likely to get him to start calling you closer to the expected time than if you yell at him.

On the other hand, there are times you don't want to enable his behavior. For example, if he's suppose to meet you at 1 o'clock to go to the beach and he doesn't show up on time, take off after waiting a few minutes and go alone or call a friend. Don't stay there waiting for him. When you see him again, don't yell. Just say you figured he got tied up and you decided not to waste the afternoon.