Questions about the Timeline and other facts...possible spoilers

I am curious about the timeline. There is a scene when he says "We've only been going together for what like 5 months..." but in the movie that is over a year after they first met....

Secondly, I am curious why he didn't lock his door. I understand initially that he was a Christian and had several close friends that often stopped by, but after she started acting crazy, why did he then still keep his door unlocked? In the birthday party scene for example somehow they all got into his place.

Third, why didn't he ever go to the police? I understand at first he thought she was just blowing off steam or it would work out of her system, but why after the tires or the letter she put on Katie's car did he still not go to them when clearly he could have had them issue a restraining order?

Maybe I'm reading too much into it but these were just a few questions I had...

The scary part is I think when I was younger I was very melodramatic about my relationships so while I was ashamed to admit it I could relate to the jealousy she felt at first. I'm glad that I had the sense of mind to not ever take it beyond that emotional hurt. Meaning beyond maybe some hurtful words, I never took any behavioral actions. I think sometimes when we are young adults we do not know how to manage our emotions, but most adults eventually out grow that phase and learn healthy ways to cope when relationships turn sour and luckily not many people would ever act out the way she did...I'm not excusing her actions by any means but I'm just saying that I felt her pain at first...Then I realized he gave her many chances to realize that he wasn't interested beyond their passion and she ignored all of the signs. I'm glad most of us see those signs eventually.