as salam alaikum
Islam is a religion with guidelines for all aspects of life. Marriage is also an aspect of life and it is regulated by the Almighty according to His divine standard. The Qur'an states that it is not permissible to marry polytheists: "And marry not an idolatress until she believes: a believing maid is better than an idolatress even though she might highly please you. And do not give believing women in marriage to idolaters until they believe. And a believing slave in better than a free idolater" (2:221). Marriage-life in Islam is not simply a companionship between two people but part of the spiritual journey to Allah where husband and wife help each other for His sake and under His holy guidance: "Help one another in righteousness and taqwa" (5:2). A non-Muslim husband or wife cannot fully understand and observe all faith-related, spiritual and sometimes moral etiquettes that a Muslim person is called to observe. Also, Islamic lifestyle in ordinary circumstances is not a path that can be traveled unilaterally by a husband or a wife alone.
It is true that in some cases there can be mutual respect and levels of understanding with a non-Muslim spouse but this is not a perpetual common ground to walk in, neither a shared path of faith leading to the same destination.
With prayers for your success.