<human>: Can you summarize the given text in a few sentences?

Me: 28, male. Her: 24, female. Duration of relationship: 6 months

Issue: Girlfriend hired personal trainer through her gym. Her personal trainer set her up with 'MyFitnessPal' (mobile app to track calorie intake). So far, so great. I also use 'MyFitnessPal'. The girlfriend logged into the MyFitnessPal website on my personal PC (not a big deal to me), used it for a few minutes to input her diet data and closed the browser. Fast forward the next day when I hop onto my PC, and use MyFitnessPal for my account, it appears she left herself logged in.

Side note: She had text messaged her personal trainer to ask him some questions regarding protein powder. To me, that's totally acceptable. Not a big deal.

Back to MyFitnessPal - she has a new message. Now, I'm outright curious at this point as I didn't even know MyFitnessPal was a pseudo-social media site. The message is from her trainer. And so is the other 14+ messages that have gone between them over the course of a week.

The messages start off harmless, but, eventually migrate to topic's that are inappropriate for a client/trainer relationship.

Here are some snippets: HIM: mostly eh :P. take it you wouldn't mind a guy you actually liked to pay for something :P I have met guys who had girls do the same and never understood that I couldn't have a girl pay for tons of stuff for me it would feel wired as hell. lol. but they were shady douche guys that I didn't get along with lol. haha well I can always repay your kindness during sessions :P

HER: so since you were a marine is it safe to assume youve been married like 3 times and have 5 kids? ;)

My thoughts: This is making me super uncomfortable. I don't know how to tackle this situation, since I technically 'snooped' on her account.
<bot>: I snooped. Girlfriend and personal trainer are messaging each other. I feel uncomfortable and don't know how to address this.