Recently I've been seeing some alarming posts about how attractive it is when a significant other is loyal in a relationship...
I'm sorry, what?
Unless you're in a consensual, open relationship where both you and your partner have agreed to see other people, then loyalty isn't attractive, it's expected.
You know what is attractive in a relationship though? When my boyfriend wears a suit. Or when he cooks me dinner because he's being thoughtful and knows I had a bad day. But ever since the beginning of my relationship, loyalty has been and always will be expected from both of us.
Sure, we both still comment occasionally about whether someone else is attractive or not but we never shove it down each other's throats because that's just malicious. It's natural to think other people are attractive and no one expects that when you're in a relationship, every other person on the planet suddenly becomes ugly.
Sometimes people think loyalty means different things. The biggest one I hear is that "flirting isn't cheating". Yes it is. Flirting is not being loyal to your significant other. It's sending signals and emotions to someone else with intentions that should not be there.
"You can look at the menu, but you can't order from it."
If you're in a relationship, you need to follow this. Loyalty is expected; it's not an option. You don't get to wake up in the morning and while deciding between which shirt you want to wear, you also decide whether you're going to be loyal to your s/o or not. That's not fair to them or you.
Because once you make that decision to be unfaithful and cheat on your significant other, even if it's just one time, you screw up their mindset and trust for the rest of their life. For every single relationship they have in the future, they'll be wondering if their new partner is going to cheat on them too.
If loyalty sounds too "hard" for you, then you need to make that clear to your partner right from the get-go or just save them the heartbreak and don't be in a relationship.