Stefan Salvatore began his journey on The Vampire Diaries as the kind of tortured hero character, and as a man who was in very sharp contrast to his gleefully villainous brother Damon. But as Stefan's character grew and more of his personality and past were revealed there were obviously elements to him that were darker and crueler than Stefan and anyone around him wanted to believe.
Stefan is a complex character with a downright immoral side to him, and over the course of his decades of living as a vampire he understandably has had moments where he made the worst possible choice or did the worst possible thing. And Stefan was a character who lived in a lot of denial about who he was, so he really wasn't able to reflect on mistakes and learn from them either. The laundry list of Stefan's misdeeds is long, but here are the ten worst things that he ever did.
Treating Caroline Like A Consolation Prize
It's actually incredibly important to remember that romantic relationships aren't the be all, end all of relationships, and The Vampire Diaries has a particular problem remembering that in most instances. In most instances, except for the relationship between Damon and Stefan. It's okay the Stefan wants to prioritize his brother over everything else, and it's even okay that Stefan sometimes wanted to prioritize Elena over everything else, but he really shouldn't have continued his relationship with Caroline if he wasn't willing to make her his priority at least some of the time. I mean, what kind of dude marries someone and decides to kill himself immediately afterwards?
Prioritizing Damon Over Everything
Stefan's willingness to put Damon ahead of everything would almost be endearing if Damon weren't such an objectively terrible person. Stefan understandably doesn't want to give up on Damon, and he rightfully feels some guilt for convincing Damon to become a vampire when he really didn't want to, but Stefan's love for Damon crossed the line into enabling most of the time.
Even in instances where Damon was completely in the wrong and even in instances where Stefan had the opportunity to stop him, Stefan almost always wouldn't do it. Their relationship is important, but it gets to a point where Stefan is hurting him more than he's helping.
Not Telling Elena About Katherine
In Elena's eyes Stefan Salvatore is very much the classic romantic hero, but sometimes it's extremely hard to understand why. Sometimes it's hard to understand how their relationship even got off the ground. Stefan wasn't attracted to Elena solely because she looked like Katherine, but the minute that Elena found out that Stefan was a vampire he should have spilled the beans and informed her that Elena's ancient identical twin was the one who made him a vampire in the first place. It was a very weird and unnecessary breach of trust that actually put Elena in a significant amount of potential danger.
Killing Vicki Donovan
Stefan and his hero hair loves to be the one to swoop in and save the day, but sometimes he takes his hero complex way too far. He is willing to do whatever it takes to protect Elena, but in this particular circumstance it really wasn't necessary to kill Vicki. Yes, she was dangerous, but Stefan could handle her, and she hadn't even been given the chance to adjust to being a vampire yet. And it was inconsiderate for Elena as well, Elena was the victim in that circumstance but living with the fact that Vicki died to save her can't have been easy.
Playing The Good Guy
In fairness to Stefan, he is someone who genuinely does seem to believe that he's a good person and for the most part he does try to be the man that he likes to see himself as. But he's objectively a terrible person, and he's even pretty bad for a vampire sometimes.
When he's contrasted with Damon it's easy for him to act like he's the "good brother", but Stefan is actually almost more manipulative and cunning than Damon is. If he feels like it's necessary he will do a lot of violent things, but he excuses them because he still thinks of himself as a good person.
Letting Damon Abuse Caroline
Because Stefan is a ripper he is always walking a pretty fine line. And if he crosses that line, things can get catastrophically bad. So it's easy to see why he is so ardent about his own self control. However, when he first arrives in Mystic Falls Damon returns too, and Damon doesn't hesitate to start messing with Elena and the people around her. And when Damon starts using and abusing Caroline Forbes, Stefan doesn't step in and instead tells Elena that he's essentially unstoppable when in retrospect that's clearly not true. And Caroline was his future wife, for goodness sake!
Making Damon Turn
Stefan deserves a little consideration for this because obviously hindsight is 20/20, but convincing Damon to become a vampire is one of his biggest mistakes in life, and it has had some of the most dire consequences of anything he's ever done too. When Stefan and Damon initially have the opportunity to turn Stefan immediately does it, while Damon doesn't want to keep going without Katherine. But Stefan convinces Damon to do it because he doesn't want to lose his brother, and because being a vampire is apparently amazing. Given what Damon's done that was obviously a mistake, but it was also a mistake because it just wasn't what Damon wanted.
Protecting Elena At Any Cost, Even When She Didn't Want Him To
As far as boyfriends go, Stefan was one of Elena's better choices in life. However his ability to actually let Elena decide what she wanted to do for herself was always a bit spotty.
There were occasions where he actually listened to what she wanted and did it even though he wouldn't have normally done the same, but there were also instances where he forced her hand when she really didn't want to do something, and worse yet there were times where he didn't even inform her of things and therefore didn't give her the option of even voicing her own decision.
Killing His Dad
So Giuseppe Salvatore was a bit of a psycho and definitely not a good parent to Damon or Stefan, and you could say that Stefan killing his father was kind of an eye for an eye since it was actually their father who shot both brothers and triggered their transition into vampirism in the first place. But still, killing your dad is not a great way to start off your brand new and exciting life. And while the initial wound to Giuseppe was accidental, Stefan's decision to drink his father's blood, become a vampire, and then watch daddy dearest die certainly wasn't.
Going Ripper And Loving It
When Stefan is on the right track he is kind of doing okay, at least in terms of the average vampire, but when he decides to go off the rails then what he does in his ripper state is ten times worse than every other horrible thing he's done combined. When Stefan is first falling off the wagon he does try to resist, but once he has let himself go he really, really lets go. Pretty much all vampires commit murder at some point, but most of them never get close to Stefan's body count and most of them definitely don't enjoy it as much as Stefan does.