甘心做你的俘虏
[gān xīn zuò nĭ de fú lŭ]
It translates to 'Willing to be your captive/slave'. In context, the phrase likely represents being willingly submissive and devoted to the object of their affection. The user is saying that despite knowing this choice might bring discomfort to them, they still decide and take pride in submitting and belonging to that special person.