Dreaming of my girlfriend marrying someone else is a negative sign as per dream meaning and interpretation. The dream means you will be insecure and jealous. You are lacking in confidence and courage. It also means unwanted thoughts polluting your mind. Dreams of my girlfriend marrying someone else mean you will realize that your life is completely dependent on another individual and this will give you jitters.
Dream of my girlfriend marrying someone else and you are present in the dream means you will witness something that will shake your personal life. It also means you will decide to walk out of an intense relationship.
Dreaming of my girlfriend marrying someone else and you see strangers only in the dream means something is happening behind your back and you are not aware of it.
If you for some reason wake up smiling or happy after the dream means overconfidence. You will take people for granted and this will result in trouble.
Please note that quite often such dreams are the result of happenings and thoughts during daytime or just before sleep. In such case the dream has no meaning. The dream to have a meaning it should happen naturally without any kind of daytime influence.