The rule of the thumb is that if someone becomes depressed or suicidal or negative or exhibit behavior that is harmful towards others, then they are doing it wrong.
One example of this from the Vesali Sutta are the monks who got too obsessed with the meditation on unattractiveness meant to overcome lust, and committed suicide. The Buddha then advised the remaining monks to switch to the mindfulness of breathing to create positive feelings, if they became negative by practising something else. This is just like driving a car - if you are veering too much to the left, then turn the steering wheel to the right and vice versa. The goal is to reach the destination safely.
The second example of this from the Alagaddupama Sutta are people who learn the teachings of the Buddha but do not truly understand it and do not practice it. Instead, they use it to attack others and defend themselves in debates. This is a philosophical obsession.
A third example from the Acintita Sutta are people who are obsessed with useless metaphysical speculations, which drive them to madness.
However, spending time alone to reflect upon the teachings and meditate, rather than having a good time with the cool folks - that's quite acceptable.
An example of this comes from the Vajjiputta Sutta:
On one occasion a certain monk, a Vajjian princeling, was dwelling
near Vesali in a forest thicket. And on that occasion an all-night
festival was being held in Vesali. The monk — lamenting as he heard
the resounding din of wind music, string music, & gongs coming from
Vesali, on that occasion recited this verse:
I live in the wilderness
like a log cast away in the forest.
On a night like this,
who could there be
Then the devata inhabiting the forest thicket, feeling sympathy for
the monk, desiring his benefit, desiring to bring him to his senses,
approached him and addressed him with this verse:
As you live in the wilderness all alone
like a log cast away in the forest,
many are those who envy you,
as hell-beings do,
those headed for heaven.
The monk, chastened by the devata, came to his senses.