Which of the following is used when a friend suggests that the key to losing weight is eating less and exercising more?

The answer is: Logos

In persuasion, Logos is a method to persuade people by using logic rather than emotion or ethical standard.

This means that persuasion made by logos will be objective, factually correct, and can be backed by scientific evidence.

In the example above, the friend suggested the other person to eat less and exercise more to lose weight. (no mention of feelings or moral). We can conclude persuasion is based on logic since in order to lose weight you need to burn more calories than you eat. This can be done by eating less and exercise more.

if your boyfriend is cheating on you, my best advice to you is to dump him, he's only going to drag you down. and if you do, don't fret there's plenty better that know how to treat a person right. i mean honestly, the whole point of a romantic relationship is love, and if you love someone you aren't going to cheat on them. i do believe in second chances, but why would he cheat in the first place? i personally feel that if someone cheats, they ruin any chance they wanted/had with you. i wish you the best of luck with this, hang in there.