Leveling my summoner

Former hero, Dorian, after tragedy struck, spent over a thousand years in a forbidden library learning all that humanity has ever achieved. Magic, swordsmanship, healing and even cultivation. However, just as he lost all hope of leaving this place, he was finally called back to Eyluania by a runaway elf, Melissa Wools. Dorian returned with burning hatred like an enraged dragon who wanted only one thing. Revenge. But how to deal with his new summoner? If she dies, he will be sent back to the library again. Only one option left… "I'll level her up!" How will Melissa survive torturous training of an immortal psychopath?