Not really much I can really say that'll actually help you in that fight, as it is by far the hardest fight in the game, as far as I'm concerned. However, I will try:
One: Set Cure to X on the shortcut menu, then always have your finger poised over the R1 button. That way, in the event you're button mashing, you only need hit R1 to heal. It's not as easy as it sounds, however, because you get interrupted during casting. You need to learn to heal a little earlier than you normally would.
Two: When he uses Dark Aura (The move where he flies around the room like a motherfucker), you can either hit square to use Guard OR jump up high and glide in a wide circle around the "arena". If you're quick enough, he won't be able to hit you. However, the glide will wear out before his move does. So, let go a little early and jump as soon as you hit the ground. It won't always work, but it's better than nothing as that move hits hard.
Three: When the floor starts letting up those explosions, run or glide around the arena in circles. Sounds lame, but it's the best way to avoid it.
Four: Take any chance to hit him you can, but always be ready to back off and heal at the sign of trouble. I've healed before Dark Aura and purposely let him hit me before just because I was so low on health that I came out in better shape.
Not exactly useful if you can't pull them off properly, but if you can, you'll be fine. Don't expect it to be easy though, even with this though. It's still hard as hell. But, I've beaten him at lower levels than 44 before. Just hope for a bit of luck.
P.S. Metal Chocobo is the best way to go at this point. Just don't miss the Oblivion in that room after the fight.