If you are role playing 'book Geralt', who is trying to get back together with Yennefer,does it makes sense for Geralt to sleep with Keira Metz? Yen already blames Geralt for the Triss affair from the past 2 games, (even though Triss obviously took advantage of Geralt's amnesia) would Geralt risk Yennefer reading his mind to find out that he had slept with yet another sorceress? lol

Yen got aggressive only on Triss, and Triss alone, regardless of what you actually did in previous games (as in W2 we were mostly deprived of any choice). Nobody else worries her in W3. That's how game reacts.
Regarding books, well, before their untimely death, nor Yen, nor Geralt were exactly "faithful" to each other, hard to say what would they do now.

I thought Yennefer in the books wanted Geralt to commit, but he kept refusing to say he loved her (because he had admitted commitment issues), she was quite annoyed that Geralt was sleeping around, especially with other sorceresses so she dubbed their relationship toxic, and tried to pursue love with other people, primarily Crach, Geralt got scared that he would lose Yennefer, so he pursued her. That ended badly (sort of) Crach was going to make Geralt fight him to the death over Yen, then Yen ran away. lol I thought near the end of the books Geralt and Yennefer were committed to each other? When I started the books I thought Geralt would be like James Bond :P (new girl every story; especially considering the time frame). Yet he slept with only a few women, two or three before Yen? Then Triss and Fringilla Vigo after the Last Wish story.

Still don't know why game Yennefer blames Geralt for Triss, when I learned what Triss was doing, I thought it was rather sad, creepy and desperate. lol

Yen: "I had mage friends help me get my memory back."
Geralt: "My mage friend did not want me to get my memory back..."
Yen: "Shut up Geralt she was my friend before I knew you, therefore it's your fault, now drop the issue."
Geralt: --_____--

XD

To be honest, I don't really remember them well, as I read them when they were released, and that was... about 15 years ago or so. Besides, two last books were rather difficult to read; some people blame Ciri for that, but my money on "I'm so tired, I don't know what to do", as game feels about the same towards the end. /grin That part is one of things I openly dislike, as Yen blames Geralt, refusing to accept his amnesia (in case you dumped her), or still chastising Geralt for Triss (if you didn't dumped Yen), and that's what I don't get: W3 apparently ignores W1 entirely, as in that save I've imported I had little contacts with Triss. After reading books I don't feel very fond of sorceresseswes ;). As I said, in W2 CDPR made decisions for us, as, apparently, even rather distant (like giving a wide berth :D) relations with Triss are ignored in W3. Also, I have some problems with timings. Yen said Geralt being "wooing the damsels" (Okay, one of them) for long time. IIRC, in W1 he spent few weeks (2?) after he was found in the forest near Kaer Morhen, then he departed to Vizima. In W2 nobody returned to Kaer Morhen, as Geralt was running around Vizima, following Foltest's orders (even if he said he dislike them, apparently he disliked them less, than Shani's companionship), and then, after Flotsam, Triss and Geralt became separated till Loc Muinne, where they part ways soon after. So, I have one question: What the fuck, Yennifer?
That alone, cute Triss shyness, and her more "alive" behaviour were enough motivation for me. /grin