Just to add a little of my own Mormon perspective, and it's just my own, but it appears to me that this guy viewed JA as a helpless little bird who was new to the gospel and that she just needed love and friendship to straighten out her life. He may believe if TA just lived his standards, JA would have a chance to reform.
In some cases, it is disappointing to see a Mormon youth compromise his standards, especially with someone he baptized. Instead of seeing them both straighten out their lives, you see them both choose another way. I can see that and I think that may be where this witness may be coming from - disappointed in Travis because he "knew better."
What this young man does not understand is that JA is a very complex personality and that there are likely serious psychological issues. She has already been proven to be a very good - scary good - liar. She can play someone like this so easily - someone who feels sorry for her who wants to "save" her. I would guess he still believes that she can reform if just given the chance.
This is so over his head. He is lucky he wasn't taken in this too. He just doesn't realize it.