She is not as wet as your ex because she is NOT your ex. She is a whole and different person then your ex. Did you ever stop and think that? I mean everyone is different. So she does not lubricate well. Help her out. A small dab of KY, tasteless odorless, goes a long way. She may need a lot more foreplay before she gets to an acceptable level of wet.
Part of the turn off might be that you are comparing her to the ex!
Ever stop and think that she might not be wet cause you are not as endowed as her ex?
She probably doesn't produce as much lubricant compared to other girls. There are girls who get turn on, but doesn't get as wet, so instead of thinking that she's lying to you, maybe you can use lubricant?
Wow, I am the same way, I am very very dry even when I'm turned on sometimes. Thereafter, my boyfriend always goes down on me first or spends quite a while in foreplay or we use lube, but I am definitely turned on.