I found it believably enjoyable. The boyfriend was a jerk. Hated the father. Bad news from the beginning. The father was "reading his mail" is why. 
I still think lying would have destroyed Lorna and Mark. When you are young, you don't understand the choices you are making for a lifetime. 
How could love ask someone ask someone to do that? 
What next? Then what if Mark decided to dump her at the altar, and she had lied for him? 
I bet she'd feel far worse.