Is it a sin to lie and hid to seek Islam?
If you are in a difficult situation where it will cause harm to you in exposing your Islam, then you can conceal your identity as a Muslim.
However, this cannot be done in marriage. The reason is that if you are a Muslim woman, then it will haram to live with a non Muslim man, and if you are a Muslim man, then it will be haram to live with a woman who commits shirk. In these cases, there will be no marriage between such people.
So, if you are a Muslim woman and your husband is a non Muslim, then you need to disclose your Islam to him. If he becomes a Muslim, then your marriage will continue. However, if he refuses to accept Islam, then your marriage with him will be terminated, since it will be sinful for you to continue this marriage.
May Allah make it easy for you.
And Allah knows best,
Mufti Waseem Khan