expression, noun
being a slave of love; weakness from being in love
Refers to the vulnerability or disadvantage one has because they are in love with someone, often implying that the other person can exploit this emotional attachment.
惚れた弱みで、彼女の頼みを断れなかった。
Because I was so in love with her, I couldn't refuse her request.
惚れた弱みにつけ込まれて、高い指輪を買わされた。
They took advantage of my lovestruck weakness and made me buy an expensive ring.
弱み is a general weakness or vulnerable point, while 惚れた弱み specifically refers to the weakness caused by romantic love.
Compound of 惚れた (perfective form of 惚れる 'to fall in love') + 弱み ('weakness'). The phrase literally means 'the weakness of having fallen in love'.