If the custom is for a girl not to marry her cousin, does he become a mahram for her?
Question

                It happens that in my country,it is not allow to marry someone cousin according to their culture,if it happens like that ,can my cousin be my mahram?.
Praise be to Allah.The woman’s mahram is 
    anyone whom it is permanently forbidden for her to marry because of blood 
    ties, breastfeeding or marriage ties. This is not based on traditions and 
    customs; rather it is based on sharee’ah. Allaah, may He be glorified and 
    exalted, has stated which women are mahrams for men, as He says 
    (interpretation of the meaning): 
“Forbidden to you (for 
    marriage) are: your mothers, your daughters, your sisters, your father’s 
    sisters, your mother’s sisters, your brother’s daughters, your sister’s 
    daughters, your foster mothers who gave you suck, your foster milk suckling 
    sisters, your wives’ mothers, your stepdaughters under your guardianship, 
    born of your wives to whom you have gone in — but there is no sin on you if 
    you have not gone in them (to marry their daughters), — the wives of your 
    sons who (spring) from your own loins, and two sisters in wedlock at the 
    same time, except for what has already passed; verily, Allaah is 
    Oft‑Forgiving, Most Merciful”
[al-Nisa’ 4:23]. 
So a woman’s mahrams on the 
    basis of blood ties are: her son, her father, her brother, her brother’s 
    son, her sister’s son, her paternal uncle and her maternal uncle. 
Her mahrams through 
    breastfeeding are the same. 
As for her cousin, it is 
    permissible for her to marry him, and it is not correct for him to be her 
    mahram under any circumstances, even if custom dictates that he should not 
    marry her.  
No one has the right to 
    regard as permissible that which Allaah has  forbidden, or to regard as 
    forbidden that which Allaah has permitted, or to claim that a cousin may 
    look at his female cousin or be alone with her, because that is contrary to 
    sharee’ah. Rather the woman must observe hijab before her cousins as she 
    observes hijab before all non-mahram men. 
Allaah has mentioned those 
    before whom it is permissible for a woman to show her adornments, and He did 
    not mention the cousin because the cousin is not one of her mahrams. Allaah 
    says (interpretation of the meaning): 
“And tell the believing 
    women to lower their gaze (from looking at forbidden things), and protect 
    their private parts (from illegal sexual acts) and not to show off their 
    adornment except only that which is apparent (like both eyes for necessity 
    to see the way, or outer palms of hands or one eye or dress like veil, 
    gloves, headcover, apron), and to draw their veils all over Juyoobihinna 
    (i.e. their bodies, faces, necks and bosoms) and not to reveal their 
    adornment except to their husbands, or their fathers, or their husband’s 
    fathers, or their sons, or their husband’s sons, or their brothers or their 
    brother’s sons, or their sister’s sons, or their (Muslim) women (i.e. their 
    sisters in Islâm), or the (female) slaves whom their right hands possess, or 
    old male servants who lack vigour, or small children who have no sense of 
    feminine sex. And let them not stamp their feet so as to reveal what they 
    hide of their adornment. And all of you beg Allaah to forgive you all, O 
    believers, that you may be successful”
[al-Noor 24:31]. 
May Allaah help us to do 
    that which He loves and which pleases Him. 
And Allaah knows best.