Question about pill cutting of finasteride 5mg tablets.

I usually cut a ~10 day supply but the last couple of months.  I feel like finasteride doesn’t do anything since I started doing this. For the first months I used to have watery semen and sometimes feel slight reduction of my sex drive but the last couple of months I have ZERO side effects and I’m curius if cutting pills causing them to lose effectiveness after some days.

It is not unusual for people on finasteride to have their body normalize and see that the side effects disappear in the first 1-3 months, much like you discussed.   If you keep the pills in a sealed pill bottle so that moisture does not get to it, then it will hold for months.