Dark God's Reviviscence By I. T. Lucas

Toven might have failed in his attempts to improve humanity's condition, but he isn't going to fail to improve Mia's life, making it the best it can be despite her fragile health, and he can do that not as a god, but as a man who possesses the means, the smarts, and the determination to do it.
No effort is enough to repay Mia for reviving his deadened heart and making him excited for the next day, but the flip side of his reviviscence is the fear of losing its catalyst.
Given Mia's condition, Toven doesn't dare to over excite her. His venom is a powerful aphrodisiac, euphoric, and an all-around health booster, but it's also extremely potent. It might kill her instead of making her better.