Reference: Fataawa Ramadhaan – Volume 2, Page 456, Fatwa No.387
Majmoo’ Fataawa Shaykh al-Islaam Ibn Taymiyyah – Volume 25, Page 265
Question: Regarding [the husband] if he kissed his wife, or cuddled her and thereby excreted prostatic fluid, does that invalidate his fast or not?
Response: According to most of the scholars, his fast is invalidated because of that.