should i prevent my friend from getting married?

i only know this girl Andy for 3 months, we are both in an overseas program from university ie we came here alone far from families friends and everythg and we met here and became friends. she met a boy from here and fell in love with him and they are planning to get married within the month... she basically knows nothing about him, its been 2months that they are dating and spending days smoking paths, she says he would do anythg for her and is the first one to show respect to her so she is sure he is the one and accepts to marry him.

they want it to remain secret so am the only one aware (i am supposed to be the witness at the wedding) but i started investigate a little and am not comfortable with them even if they seem perfectly happy (no wonder they are happy smoking path) but what about the long-term vision, his weird family, interests in wedding, her 20yrs old and far from parents etc. In the other hand who am i to prevent that (we only know each other for 3months) i told her my worries she told me she is positive he really loves her so who am i not to believe in the "love at first sight" thing?