It's hard to say, really. Lymnieris is very associated with sex, but is perhaps best though of as the deity concerned with the sanctity of consent. That's a neat area of concern, but not one really encouraging of punishment or curses.
The two obvious avenues I can see are an inability to perform sexually, which would be interesting but perhaps not appropriate in this particular case, or becoming deeply unattractive, perhaps showing obvious sores of one sort or another. The symptoms of advanced syphilis without it actually being transmissible to others, perhaps.