Your bf screwed up by deleting those messages. If you trust him it’s okay to let him wingman for his friends. It doesn’t have to be untoward, it is just a way to support a friend. Even if other woman are involved, he doesn’t have to do anything wrong to help out. As long as you are okay with him carrying on normal conversations.

That being said, the deleted messages are a bad look (even though he is probably telling the truth about what they said), it was a boneheaded move.