Praise be to Allah.
Firstly: may Allaah reward you for your belief that Allaah alone knows the unseen this is what we hope for you and for every sincere Muslim woman and this is one of the essentials of faith in Allaah Alone.
But we wonder how, after saying this, you can be afraid of one who knows nothing of the unseen?
You have to be assured and put your trust completely in Allaah, for nothing will happen to you except that which has been decreed by Allaah.
The ruling on fortune-telling, i.e., soothsaying, and claiming to know the unseen, is that these are actions which condemn a person to Hell and put him beyond the pale of Islam.
Fortune-tellers cooperate with the jinn; they are liars who cooperate with the shayaateen (devils), who do not help them except after they have changed their religion, and whoever changes his religion [leaves Islam] is to be executed. The ruling concerning those who go to them and believe them is that they are guilty of kufr; if they do not believe them, their prayers will still not be accepted from them for forty days.
The evidence (daleel) for the former is the hadeeth of Abu Hurayrah, according to which the Prophet (peace and blessings of Allaah be upon him) said: Whoever goes to a fortune-teller and believes what he says, has disbelieved in what was revealed to Muhammad.(Narrated by al-Tirmidhi, 135; Abu Dawood, 3904; Ibn Maajah, 639; Ahmad, 9252. The hadeeth was classed as saheeh by al-Haakim (1/49), and al-Dhahabi agreed with him. Al-Haafiz ibn Hajar said, it has two corroborating reports narrated by al-Bazzaar with good isnaads. See al-Fath, 10/217)
The evidence (daleel) for the latter is the report from one of the wives of the Prophet (peace and blessings of Allaah be upon him), who said: the Messenger of Allaah (peace and blessings of Allaah be upon him) said: Whoever goes to a fortune-teller and asks him about anything, his prayers will not be accepted for forty days.(Narrated by Muslim, 2230).
How the fortune-teller gets his information was explained in the hadeeth narrated by Abu Hurayrah, in which the Prophet (peace and blessings of Allaah be upon him) said: When Allaah decrees a matter in heaven, the angels beat their wings in submission to His words, making a sound like a chain striking a rock. When the fear is banished from their hearts, they say, What is it that your Lord has said? They say: The truth, and He is the Most High, the Most Great. Then the one who is listening out hears that, and those who are listening out are standing one above the other Sufyaan [one of the narrators] demonstrated with his hand, holding it vertically with the fingers outspread. So he hears what is said and passes it on to the one below him, and that one passes it to the one who is below him, and so on until it reaches the lips of the soothsayer or fortune-teller. Maybe the meteor will hit him before he can pass anything on, or maybe he will pass it on before he is hit. He tells a hundred lies alongside it, but it will be said, Did he not tell us that on such and such a day, such and such would happen? So they believe him because of the one thing which was heard from heaven.(narrated by al-Bukhaari, 4424).
When the Shaytaan listens out to hear what the angels say to one another about the decree of Allaah, this is part of the knowledge of the seen, it does not not mean that the shayaateen have knowledge of the unseen. Then they add a hundred lies to that word, such as when a fortune-teller says that So and so will give birth to a boy, and the people see that he was right about that so they believe in him, but he adds lies about the child, saying that he will get married in such and such a year and will die in such and such a year and other such details. So he gains a high stature in peoples hearts and they seek to get close to him by bringing him gifts and money, and he makes a profession out of these lies when the people believe in him, and so he makes a living by haraam means.
Not every fortune-teller is a kaahin (soothsayer). He may be a geomancer or reader of coffee-cups, because the kaahin, unlike the others, is one who receives information from the jinn. The others are just liars, but the same ruling applies to them, because they claim to have knowledge of the unseen, although the kaahin who cooperates with the shayaateen is more of a kaafir because the kufr of fortune-telling is compounded by the kufr of his interacting with the shayaateen, who do not give him what he wants until after he directed some acts of worship towards them in a manner which takes him out of Islam.
You have to advise your mother not to go anywhere near these liars, lest she falls into sin or her good deeds are wiped out. Do not give up the idea of marriage, because marriage brings many benefits. It is an important matter which is part of the fitrah (natural inclinations of man) and of the religion. Your life will not be miserable, in sha Allaah; be optimistic and hope for a good and happy life. We ask Allaah to join you with a husband who is knowledgeable and righteous.
If something bad happens, and you marry someone with whom you are miserable, this is because of the decree of Allaah (qadaa and qadar), not because of what the accursed fortune-teller said or because he knows the unseen. This may happen as a test or trial. In any case, going ahead with the marriage in addition to its own great benefits will be a way of snubbing these liars and fortune-tellers, and those who believe in them. May Allaah help us and you to do all that is good. May Allaah bless our Prophet Muhammad.