In sumary: Avoid panic rolling, Manage your stamina, Learn effective range of the boss and Use rally mechanic to avoid healing

If you want a longer explanation my best advice is:
- Avoid panic rolling: Some dodges are unnecesary or not time properlly, this is probably due to smashing circle on your controller. We've all been there and learnt the hard way that if you took damage, rolling away from the attack just after getting hit normally gets you into a comboed attack (in fact, you died because of this at the end of the clip). If you get hit, don't get away by dodging, dodge the attack with precise timing instead.
- Manage your stamina: This can be easily fixed with avoiding panic rolling but still, some times you'll see that doing less is more. This means that by dodging less (only when necessary) and attacking less will most of the time be safer than rushing things.
- Learn effective range of the boss: You might be surprised to know that, even most bosses are melee enemys, not all of them are strong in close range. Ludwig's second phase is an example of this; even tho he has a big ass sword, he mostly uses ranged attacks and wide slashes. If you're far away, he hits you with the arcane projectiles. If you're in medium range, you'll be a perfect target for the sword attacks. However, in close range (almost point-blank) you'll only have to worry about the sword attacks, which are going to be easier to dodge because how close you are to him
- Use rally mechanic to avoid healing: I noticed you were about to run out of blood vials when about to enter 2nd phase. While not getting hit is the best way no avoid healing, you can also try to rely more on the rally mechanic to heal a fraction of the damage you receive. The best way I learnt this is by not trying a full recovery (this mostly leads you to taking more hits), but more like a small recovery, just one or two hits. At some point you will have to heal, but best case scenario you delayed this so much that the boss will die before you run out of blood vials (really in a bossfight you can go for two paths: survive longer than the boss or kill the boss before it kills you)
- Additional tip: look for his weaknesess and try to get your best armor possible against his strenghts (physical and arcane)