have a weakness for (someone or something)
To have a special affinity for someone or something; to find someone or something irresistible. I have a weakness for candy bars, so Halloween is my favorite holiday. Jon has a weakness for redheads, so of course he's dating another ginger. Stu has a weakness for Patty, so I'm sure he'll clear his schedule once he hears she's in town.
have a weakness for someone or something
Fig. to be unable to resist someone or something; to be (figuratively) powerless against someone or something. I have a weakness for chocolate. John has a weakness for Mary. I think he's in love.
have a weakness for
Be susceptible to; also, like or enjoy. For example, She has a weakness for older men, or Bill has a weakness for fine wine. [c. 1700]