It's challenging to pinpoint the exact reason for your boyfriend's change in behavior without more information. However, there are several potential reasons why this could happen:
Peer Pressure: Your boyfriend might feel influenced by his best friend's behavior or attitudes, leading him to act differently when his friend is around. He may try to fit in with his friend's personality or be swayed by his friend's opinions.
Insecurity: Your boyfriend may feel insecure or competitive around his best friend, which could lead to him acting out or trying to impress his friend at your expense.
Different Social Dynamics: Some people act differently in group settings than when they are alone with their partner. Your boyfriend might feel more comfortable or relaxed when it's just the two of you, but his behavior changes in the presence of others.
Prioritizing Friendship: Your boyfriend might prioritize his friendship with his best friend over his relationship with you, leading him to ignore or mistreat you when his friend is around.
Seeking Approval: Your boyfriend could be seeking approval or validation from his best friend, and this might affect how he behaves towards you.
Unresolved Issues: There might be underlying unresolved issues between your boyfriend and his best friend that influence their interactions and, in turn, affect his behavior towards you.
Regardless of the reason, it's essential to communicate openly with your boyfriend about your feelings and concerns. Try to find a calm and private moment to discuss the situation with him. Express how you feel when his behavior changes around his best friend and ask him about his perspective on the matter.
Communication is key in any relationship, and addressing these issues openly can help both of you understand each other better and find solutions together. If your boyfriend truly cares about your feelings and the relationship, he will be receptive to discussing the matter and working towards a resolution.