I'm a 28 years old guy who is dating a 22 years old girl, who just graduated with her bachelor's degree. We have been dating for nine months. I'm a Christian. We don't attend same church. At the moment she is not getting along with me and she is considering terminating our relationship following the prophecy she was told by one of the pastors within the church she attends. The prophecy was that she would get a job, and find the right boyfriend who attends same church with her within three months.
She said the prophet went on and told her the description of the guy who is going to marry her, which in every description is the opposite of me. He also told her the kind a car she would buy. I tried to let her know that I'm here to stay and I am not going to do anything to jeopardize our relationship; I want to marry her and make her my only wife. What she said to me was that the prophet was shown this by the God with the intention to protect her because she is not in a safe relationship.
Can you please tell me how can I assure her that I am the right person for her? Could this be a true prophecy or the prophet wanting to send the guy he described to her?
It is not a true prophecy because prophecy has ceased. "Love never fails. But whether there are prophecies, they will fail; whether there are tongues, they will cease; whether there is knowledge, it will vanish away. For we know in part and we prophesy in part. But when that which is perfect has come, then that which is in part will be done away" (I Corinthians 13:8-10). For more information, see What is your proof that prophecy has ended?
As you noticed nothing that was told to your girlfriend is out of the ordinary. Of course a person who just graduated from college is likely to find a job. He clearly is describing a man within his own church whom he has in mind encouraging your girlfriend to marry. By stating upfront what kind of car she is going to buy (a large purchase typically made by someone with a new job), he influenced her decision. This sort of thing is the kind of thing county fair psychics claim to do. It isn't how God showed Himself to operate with the Bible.
But you are not likely to convince her otherwise. She would rather be lied to by a false prophet than to be with you because that prophet is telling her at least some things that she wants to hear. She is willing to give up some things, such as you, to gain what she thinks will be greater things. You could wait until it turns out that the things this man states are shown to be false (which may or may not happen), but the likely result is that she will have some other reason to claim that the prophecy had changed.
What I would suggest is finding a woman who loves you and truly follows God and not men.