It's wrong to tell secrets to your friend's partner.
Jenna sees her friend Alanna smoking, even though she reluctantly promised her boyfriend she'd quit smoking.
Jenna wants to help her friend.
Jenna tells Alanna she knows she's been really stressed lately, and she (Jenna) won't tell Alanna's boyfriend.
Jenna tells Alanna's boyfriend in the name of improving her health.
Alanna hugs Jenna and thanks her for being so understanding about this.
Alanna trusts Jenna less and stops telling her anything really personal.