What is the ruling on the fast of one from whom something was discharged during fasting, and he is unsure whether it is semen or pre-seminal fluid, taking into account that he is afflicted with excessive waswas (obsessive whispering/doubt)?

Semen has distinct characteristics, and not every discharge of semen invalidates the fast. As for pre-seminal fluid (madhy), its discharge does not invalidate the fast, according to the more preponderant opinion. Whoever experiences a discharge should verify what it is to know whether they need to perform a full ritual bath (ghusl) or ablution (wudu'). It is not permissible for them to neglect verification if they are certain that something was discharged. If they doubt whether anything was discharged, the default is that nothing was discharged. If they are certain that something was discharged but doubt whether it is semen or pre-seminal fluid, they may choose between the two. If they doubt the validity of their fast, the default is that it is valid. The cure for obsessive whispers (waswas) is to disregard them.