She suggests Juliet should forget Romeo and be happy with her marriage to Paris. She tries to guide Juliet, like a motherly figure would, but her advice could be seen as a betrayal.
The phrase 'I think' suggests the Nurse knows Juliet well and knows what Juliet wants (perhaps better than she knows herself).
The Nurse has to respect Lord Capulet's decision, as he is her employer. Respect and status wins over love. What advice does the Nurse give to Juliet regarding her marriage to Paris?