People change, even those who are very close to you will tend to change as people change their attitude if they don't like what they see in their life and environment. You should ask yourself, is there something wrong. If your girlfriend starting to disrepect you, you had done something to make her do it to you. Have you done something? What kind of disrespect she is acting against you? If you think you did nothing wrong, maybe you should personally ask her. This not comfortable for sure, but you need to confront her on the reason why she is acting that way. If that is your problem right now, then you need to solve it. No one should be disrespected. You should analyze yourself too, maybe you there is something wrong. You can only know if you ask her.