Praise be to Allah.
Islam does not prevent marriage to a Christian woman if she is chaste. Allah says (interpretation of the meaning):
“…The food (slaughtered cattle, eatable animals) of the people of the Scripture (Jews and Christians) is lawful to you and yours is lawful to them. (Lawful to you in marriage) are chaste women from the believers and chaste women from those who were given the Scripture (Jews and Christians) before your time when you have given their due Mahr (bridal-money given by the husband to his wife at the time of marriage), desiring chastity (i.e. taking them in legal wedlock) not committing illegal sexual intercourse, nor taking them as girlfriends…” [Al-Maa’idah 5:5]
What is meant by chaste women is that they are free (not slaves) and chaste (not loose or immoral).
See also question no. 2527
But if a woman is not chaste, and she has boyfriends or lovers with whom she is intimate, then Islam forbids marriage to her, whether she is a Muslim or a woman from among the People of the Book, just as it forbids marriage to a man who has girlfriends or lovers, to protect married life from collapse and to protect against mixing of lineages and to avoid causes of dispute, accusation and suspicion.
With regard to the Muslim husband attending marriage parties according to the Christian tradition, this is not permissible because there will be many things in these celebrations that are forbidden in Islam, such as free mixing between men and women, listening to music, drinking alcohol, dancing etc.
We ask Allah to help you and guide you to the religion of Islam. Praise be to Allah, the Lord of the Worlds.