There is something so ironic about Pantalone when it comes to his relationship with Dottore.
The man who always adds a loophole in the contracts to have the advantage, the man obsessed with fair exchange, it's the same man that accepted a relationship where he isn't the one with advantage over the other, Dottore. He can have benefits, and he is the one in power of the money for Dottore's proyects, but that power is nothing compared to Dottore's power over his life. A power close to the divine, unlike his mundane power.
But Pantalone was fine with it, he decided to be in a relationship despite losing a lot, and it's not about money. It's about the loss of Zandik and his segments. He would endure it, bc the benefits of the relationship are bigger for him than how hurt he can feel. The benefits are more than the elixir of immortality or having Dottore as some scapegoat for him, the true benfits are emotionals, the benefit of being alongside someone he feels connected to.
Arlecchino's voice line about him seems pretty accurate. She would say Pantalone lacks "clarity", that his actions are governed by his feelings. She talks about how people like Pantalone, rational people, would believe they're capable of controlling their emotions and that confidence is actually their greatest weakness. Then we have Pantalone talking about his relationship with Dottore in transactional terms, only for him to have acts and certain dialogues that obviously suggests more, acts and phrases that show his emotions towards Dottore. He would go to Sumeru despite field work being risky for him, despite the whole decision of going there to help Dottore being risky. He would remind Dottore of the human he is, he would express he doesn't want him to die. His emotions slips between his words and actions.
The irony of choosing a relationship, a contract where he is at disadvantage in a certain way, where he could loss something important (and he did) But he trusted Zandik, trusted him enough to let him have the power over his life and death. He has to pay for it, he would do it, he is paying for that with the painful grief. That wasn't a totally rational decision, that was an emotional decision.
But why he wouldn't trust Zandik? After all, when the gods ignored him, Zandik was the only one that looked at him, and gave him an opportunity the gods never give despite how much he desired it.
Having a vision is to be special in some way, it's a divine power. Just like Feofan could see the human in Zandik, Zandik could see Feofan as special. That's a benefit, how Zandik makes him feel is his most precious benefit. And that's why Feofan would choose to be with him, because he truly likes Zandik, even if Zandik himself can't believe him.