If I am a Shia girl married to a Sunni boy who doesn't want me to do matam (mourning) only, should I follow my husband or perform the matam no matter what?
Briefly speaking, to the best of my knowledge and based on what I found as a ruling, there are two items that the wife must have the permission of her husband. One of those items is related to the exit from the home. (Although there are some exceptions that the wives don’t need the permission of their husbands…). But in what you inquired as your question that
If I am a Shia girl married to a Sunni boy who doesn't want me to do matam only, should I follow my husband or perform the matam no matter what?
As a general ruling, Matam for Imam Hussain (a.s.) is a good deed and actually it is permissible in common conditions. But except some items, you are not allowed to get out of the home without the permission of your husband (according to Imam-Khomeini,Tahrir-al-Wasilah) even for matam. Because matam is not considered as a wajib practice that… / you’d better endeavor to obtain his consent or at least you can do matam at home in order to being in… Then I strongly belief Allah will give its complete reward to you as you observe your husband's right (permission). God willing
in shia ism takhaya is allowed meaning u can follow ur religion under cover. if ur husband is sunni and doesnt like like matam n mourning dont do it as going against husband is not permissible by Allah and thats y if u do it will be gunah also husband will stop loving you. BUT YOU CAN DO IT WHEN HE IS NOT AROUND AND DOESNT KNOW ABOUT LIKE IF HE OUT OF HOME.THEN U CAN DO IT CRY N DO MATAM THATS FINE