You make me read a lot of things
Liam's lack of attention isn't the only reason.
It is above all that she has only known him since college.
Even if she was spinning the perfect love, her curiosity would not have been satisfied because she did not have the good or bad experiences that we all need to have to pass to adulthood. Of course, she's a wife, she's a mother, but in her mind it's still young Sophia.
If she's been in need of attention for 15-20 years and hasn't had a serious conversation with Liam about it. It is because she does not have the mental age to do it. Otherwise a adult woman would have had this conversation with him, and if he hadn't changed his behavior, she would have cheated on him a long time ago.
She doesn't know how to deal with her emotions (she is embarrassed and horny at the same time), set limits, have an adult behaviour. ( And that's why we love her

)