Geralt was a part of it, and he had a right to know what was going on.
You have to remember that it is always our player perspective. From our perspective, being all-knowing Death march soldiers with the guide, 150,000+ crowns in riding bags, a full bestiary, alchemical list, and a pantry on our back larger than all the larders in Novigrad, Velen, and Skellige combined, Geralt needs to know.
From everyone else's perspective, Geralt is simple(r), stubborn and sometimes violent. He isn't told things, partially because he doesn't want to hear them (politics), and partially because people are afraid of his reaction (Ciri). Geralt is so protective of Ciri during the game, that he can actually suppress her. This is why people can get the bad ending; that is what the (partially) nonsensical decisions in the game meant.
You are supposed to trust Ciri, trust that she can make her own decisions (regardless of Phillipa, Avallach, etc.), and believe in her. As Ciri says, "This is
my story." Should Ciri really be compelled to tell her very protective, lately absent father, who has recently reunited with her, that she's planned all this up to (suicidally) run through a portal? I love Geralt - but it's a leap of faith.
The narrative hinges on the fact that Ciri makes the decision on her own. Avallach can only influence the decisions up to the tower. And even then his influence is limited. Her resolve (created by Geralt's reactions) is what pushes her through the frost.
I think the difficulty with Avallach is two-fold. First, we would like Ciri to be happy. She likes him, so some of us hope that he would like her. It isn't only the she-elf's jealousy on display in the laboratory. She's really, really mad -- threatening to flatten the place, mad. You don't get that mad at someone's secret lover telling you insults you've already heard, and possibly doubt the legitimacy of, unless you really care about that someone. Geralt can actually accuse her of this during the lab, to which Yennefer shakes her head, and Ciri continues storming.
Second, Avallach doesn't ingratiate himself to Geralt, and as consequence, the player. The nicest he is to Geralt is Through Time and Space, where he pontificated about sandcrabs, lost Geralt in a swamp/ocean/mountains, and bothered to go light the lighthouse. (Notice, it's a one-way trip from Ge'els back.) He spends most of his time with his nose in the air, waxing profound about the glory of the elven master race, and hiding valuable information about his plan for Ciri.
Given the additional context from lab and books, it's miraculous that anyone has a nice word to say.
But, Avallach isn't in love with Geralt.