One possible word that can fill in the blank is few. This word means a small number of something, and it can imply that the person did not have enough friends or social support while studying abroad. For example:
He didn’t enjoy studying abroad as he had few friends there.
He didn’t enjoy studying abroad as he had few opportunities to interact with the locals.
Another possible word that can fill in the blank is many. This word means a large number of something, and it can imply that the person had too many friends or distractions while studying abroad. For example:
He didn’t enjoy studying abroad as he had many friends there.
He didn’t enjoy studying abroad as he had many parties to attend.
There may be other words that can fit in the blank, depending on the context and the meaning of the sentence. However, these two words are the most common and logical choices. I hope this helps.