Have you read the books? Geralt has sex a lot, yes, but it’s nowhere near to the extent the games would have you believe, and whenever he and Yennefer are “on”, he doesn’t sleep with anyone else. There’s also not nearly as many sexual encounters there as there are in the games - that’s just one of those things established in the games.
And no, they’re not in love because of the wish, and that’s an interpretation that solely exists in the games. In the books they fall in love before the wish and the nature of the wish itself is different. The result of it is that their destinies are tied together - Geralt wished for it so that she wouldn’t die at that moment because she’d otherwise be dead. The main result of that is that their lives are linked and one can’t die without the other. They also keep bumping into each other even when they try to stay away, plus this has also linked Yennefer’s destiny to Ciri, since she was destined to Geralt. At no point is romantic love mentioned to be a result of the wish, and it’s clear that the reason they are together is that because throughout the literal decades that the novels span they’ve actually both matured and influenced each other to the point that they really just don’t want to live apart and they’ve both made each other better people. Yennefer literally dies in a futile attempt to save Geralt by the end, which is something beyond what any wish could ever have led to.
As much as I love the games, I can’t help but resent what they did to Geralt and Yennefer’s relationship and how the fandom views it. Triss was introduced as a love interest in 1 - which she never was in the books - because the writers “couldn’t understand why anyone could ever be with such a terrible nag”, which not only makes them seem clueless but also kinda sexist. And then when they finally brought her back in 3, they need to make the two options seem a little closer together in terms of value, so they pretty much just reduced the incredible relationship they had to the wish and made Yen’s relationship to Ciri nearly non-existent. I’m glad they dropped the Yennefer betraying them for the empire plot because that would’ve just been an absolute character betrayal, but shades of that ambition they gave her still longer. Yen never cared about the lodge and their political machinations and in the end she just wanted nothing more than to be with her family. Thankfully, he epilogue scene in Blood and Wine brings that back.