I just don't know.

My boyfriend has been helping out one of his female friends with her relationship with his best friend. He claims she has no one else to talk to about this so I let how much they've been communicating slide. They've been friends before their relationship, he even set them up together. I'm just completely uncomfortable with the fact that they literally talk from the moment he wakes up to the moment he falls asleep. He also claims that their conversations are 90% of them talking about "how to get his best friend to change" yet... he keeps all their texts between them private. He won't even open a text from her in front of me. Not only that but I seen him send a text to her then delete what he said. It's extremely excessive and I'm beginning to think something is up. Just need advice on what to do at this point.