I really hate to say this because it's pretty unkind, but do you know for sure she is pregnant in the first place? It sounds like (from reading some of your past blog posts) that L has, in the past, wanted more from your relationship then you could give her. It also looked like you guys were breaking up or taking space or becoming friends. I would be worried about someone causing drama to be more connected to you.
It seems strange that she didn't bring it up until she was upset that you had been in town and not seen her.
Has she talked with you about how she managed to get pregnant while on birth control? Or why it took her so long to tell you? Have you been to the doctor with her? Have you seen anything that proves she is pregnant? You said you hadn't been with her for two and a half months before she told you, does the expected due date match up with that?
I know these are horrible questions and you know her better then any of us but something feels strange about this to me. I would be worried that she intentionally got pregnant or is telling you she did to keep you in her life.