Oka likes Yana and wants Yana to be happy even if it's with someone else, so shes angry that Banri is hanging out with Linda which could potentially ruin Yana's happiness which is already in the dumps.

Banri doesn't want to tell his friends about the situation now because then it would be like openly admitting that he has been hiding his secret because he doesn't trust them but actually he hadn't come to terms with his past at the beginning and was running away from and avoiding his past. Now that he accepts his past, it's very hard to tell his friends about it after all this time.