我不敢给你一辈子的承诺
[wŏ bù găn jĭ nĭ yī bèi zi de chéng nuò]
'I dare not make you a lifelong promise' reflects prudence and caution regarding long-term promises or commitments. Possibly because this person understands that life is full of uncertainties, so he chooses to stay realistic about romantic commitment instead of offering unrealistic assurance. There could be fear mixed in with love, concern over not wanting to break a hasty vow.