Is there any slight difference between these two sentences?
- You cannot drink it alone. and
- You cannot drink it by yourself.
Yes, a slight difference, more in usage than in grammar terms.
You cannot drink it alone.
means wanting to drink with other people around. More common would be:
You cannot drink alone.
(Someone walks into the bar and wants to join you, and insists) You cannot drink alone.
You cannot drink it by yourself.
means you need someone's help to finish the drink. For example:
That is a large bottle of wine. You cannot drink it by yourself.
Of course then two people are involved so you are not alone. In any case, it is ambiguous without context.
Both of these statements carry two meanings which are the same. How they are to be understood depends on the context that they're used in.
They could mean:
You cannot drink it alone can also have a third meaning: