I'm a Moroccan student in the US. I'm in a relationship with a girl for 2 months now. My question is: Is it legal to marry this girl even she is not Muslim?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If the girl you are asking about is chaste and from the People of the Book then you may marry her. Allah Says (what means): {(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...} [Quran 5: 5]

If she is neither chaste nor a Jew or Christian, then marrying her is forbidden. Allah Says (what means): {And do not marry polytheistic women until they believe. And a believing slave woman is better than a polytheist, even though she might please you. And do not marry polytheistic men [to your women] until they believe. And a believing slave is better than a polytheist, even though he might please you. Those invite [you] to the Fire, but Allah invites to Paradise and to forgiveness, by His permission. And He makes clear His verses to the people that perhaps they may remember.} [Quran 2: 221]

However, do not forget that a believing girl is always better than any other one.

For more benefit, please refer to Fatwa 82067.

Allah knows best.