My girlfriend is immature, a flirt...

I have been in a relationship for almost 3 years, but my girlfriend and I fight a lot. We don’t seem to understand each other. I think she is immature and always talking about silly things. She flirts with boys as well. She always blames me in every situation and has also been disrespectful to my mother. She also blackmails me into doing things for her. Please help.
— Mohit G
The first thing you should consider doing is not refer to her as immature, because that instantly puts you in a position of moral superiority and does her a disservice. You raise some pretty serious allegations against her, and the three years you have both spent together don’t appear to have helped create a stronger bond if you maintain a lack of understanding. I suggest you think about what you want from this relationship and have a conversation with your girlfriend about how she sees it. If she is disrespectful towards your family members, find out if that is her way of hurting you and why she feels the need to do that. If you have been together for so long, there must be something still keeping you both committed to this, and it is important to find out what that is. If there is no good reason for you to be together, you won’t know unless you both share your honest opinions. This doesn’t have to be a bad thing, provided you can both acknowledge that there are problems and then talk about whether you want them to be fixed.

My boyfriend’s best friend recently made a pass at me and then told me not to mention it to anyone. I don’t know if my boyfriend will believe me, and I don’t want to cause any problems between them. What should I do?
This depends upon how you feel, and whether you want to ignore it and move on. If he doesn’t respect his friendship with your boyfriend, that may become obvious soon enough.