His insta kill fire nova can be dodge rolled like in dark souls, should help you a lot :)

I have figured that part out ( finally !!! ) but his attacks are also dropping my health quickly and run out of health before I get him down during third fight .

If you are under levelled or lack gear and dps he will tear you both a new one!
Two options... go and redo some areas and level a few more times or set difficulty to "Story" and just get past him that way.

He's honestly the toughest boss in the game in my opinion.
Some tips I can add for you to the already existent list:

1- kite him. This should be obvious, but you have to kite some of his bigger abilities and wait for him to spawn smaller mobs to refill your health potions with.

2- Movement abilities. Every character should have at least one and you definitely want to save them for getting away from his bigger hits. (running out of dodge rolls is easy)

3- healing abilities. If your mage doesnt have it already they need the healing spell, and if the rogue doesnt have it I recommend using blood for blood with regen enabled. This will help you save your potions for when you are really in trouble, which can make a big difference.

4- He dashes around quite a bit. Save your biggest skills for the times when he has stopped moving. Play the long game, and whittle him down while just focusing on not getting hit. It does require more skill to stay alive in this fight longer, but once you understand his patterns it shouldnt be that hard to do. Also make sure not to be next to him when he recovers from armor break, or save your mobility skill to get away quickly.

5- As someone else already said, improve your gear or level up. It IS possible to rush through the game to the point where he's basically impossible, but even as a fairly difficult fight he should be beatable. Sometimes it took me multiple frustrating tries to get through him, but I've managed it on every class type so far.

6- Just keep trying. He really is a tough boss, and sometimes you just have to keep at it until you get your dodges perfectly. Do your best not to die AT ALL until his third form so you have your three revives for that form exclusively. I don't think I've ever actually beat him on the first try with any of the characters I've played, and I'm notorious for restarting games like this over and over again (pretty sure between offline and online I have 10 characters now, a bunch of which are 20+ in level. I do this so I can try different play styles and see what i like best). Even playing sword and board with full block he was tough as hell.

Good luck, and keep at it!

My stratagy that worked best out of all of my characters was a Pistol/Artifact build focusing on Pets.
I mostly used Whailing Arrows to damage him. Just fire and forget.
Livor Mortis can tank him very well. If he kills it, just respawn it.
The two types of Zombie summons (Hunting and Feeding Swarms, I think they are called) add some nice damage and take the heat off of you by attracting the attention of his adds.
Keep your Summons up (espicially Livor Mortis), dodge, and keep Whailing Arrows going right on top of him.
That will kill him quickly enough.
As to your personal survival, this build works perfectly well when putting all points into Toughness. This helps a LOT. It's a real game changer.
With this build I prefer to focus on Rouge gear types.
Anything with Passive Dodge on it should be a #1 priority. It is very, very rare at that point in the game.
Get high HP and Energy Shield numbers. This works well with your high toughness score to further up your survivability.
As for Passives, I went strait for Child of Fury, the skill node that makes you regenerate Rage instead of Wisdome. Also, there is one that gives you Global Life Leach. Go for that too. In fact, try to get as much Life Leach as you can, using Gems.
Another very, very Boss useful skill (I do not remember the name) allows you to Dodge-Roll through enemies. This prevents the adds from stopping you in your tracks so the boss can one shot you.
I've just beaten the Act Two boss (for the first time ever!) at level 35 without dying once for the whole game, so it can't be that bad a build.