Feeling more comfortable socializing with a specific person, such as your boyfriend, doesn't necessarily make you antisocial. Social preferences and behaviors can vary greatly from person to person, and there's a wide spectrum of social interaction styles.
It's possible that you are introverted or have a small social circle, which can lead to a stronger preference for spending time with your partner. Introverts often find deep connections and meaningful interactions more fulfilling than large social gatherings. This is entirely normal and doesn't mean you're antisocial.
On the other hand, if you actively avoid social interactions, have difficulties connecting with others, or experience significant distress in social situations beyond just preferring your boyfriend's company, then there might be a possibility of social anxiety or other social-related challenges.
It's essential to remember that social preferences can change throughout life, and what's most important is that you feel content and comfortable with your social interactions. If you ever feel like your social tendencies are causing distress or interfering with your life, you might consider seeking support from a mental health professional who can provide guidance and help you explore your feelings and preferences more deeply.