If you’re only using a partial pill, it needs to be tightly wrapped back up
Always, always use gloves when cutting a pill - humans should not come in contact with the drug.
If partial pill dosing is a long-term thing, it may be worth looking at compounding from a reputable pharmacy. You’d need no more than 30 days worth as it does degrade some. But if you’re just partial-dosing on the way to using a full pill, not worth it.