Idealizing to me means that you're not seeing any of the flaws a person has. Not idealizing them doesn't necessarily lead to being angry with them, frustrated and so on, but it can.

As an example: I know my T is sometimes wrong about things. Sometimes he says things that are either old-fashioned, he isn't informed about something correctly. Sometimes he forgets stuff I tell him.

In phases where I idealize him, I don't really remember that. I'll take each and every of his words and they are the truth. I'll think that he'll never, ever forget about this minor detail that I told him 3 years ago.

In those situations I might get angry when he does forget something, but usually it just reminds me that I kind of idealize him and that he's just human. I've rarely ever been angry with him, but I'm pretty sure I idealize him most of the time.

So to answer your question: are there any flaws that L has which you acknowledge, know about, accept? If so, you're probably not idealizing her (at the moment). If you can't think of a single flaw, I'm kind of inclined to say that you're probably idealizing her, based on the fact that most humans have lots of flaws.