This may be slightly far fetched.. but when Tyrion met with Cersei, there was emphasis on her guilting him over the deaths of Tommen and Myrcella. Then she does the whole pregnant belly rub... and his demeanor changes when he says "you're pregnant." That's all we see.
When she talks to Jamie, she starts off with "I always knew you were the stupidest Lannister." Maybe there's more to that than just a minor insult. Either she's admitting that Tyrion is clever in his betrayal of her family (doubtful) or he has seen that the only future for Westeros is through the Lannisters and her future baby. She may have offered the chance to make things right for her baby, and thus the chance of redemption, to Tyrion... in exchange for not killing him on the spot and going on to betray Danaerys. In his mind he justifies it because Danaerys isn't able to have kids (so he thinks), so any success she achieves is short-lived. When Targaryen incest is going down, maybe he appears distressed because he's realizing that maybe Danaerys actually could have a kid, making his plan to betray her less sound.
Probably all BS...