How can one reconcile not falling into the unlawful (haram) and avoiding loneliness and pain, taking into account the difficulty of returning to one's homeland, the non-Muslim girl's refusal to embrace Islam, and the inability to marry at present?

Marrying non-Muslim women is not permissible, except for women from the People of the Book. Buddhism is among the most egregious of disbelieving faiths, and an illicit relationship with a Buddhist woman is a greater sin. Muslims and people of the Book are found everywhere, and seeking what is lawful is an obligation. Marriage is the legitimate means of safeguarding one's chastity, and for those who cannot marry, fasting is recommended. It is not obligatory to obey one's mother if she forbids marriage, especially if there is a fear of falling into unlawful acts. God's earth is vast, and it is not permissible to wrong oneself by committing forbidden acts. Loneliness can be addressed by reciting the Qur'an and seeking knowledge, for the best companion is a book. A righteous companion is better than loneliness, and loneliness is better than an evil companion.