I get why your mad. But are you forgetting his past? He isnt human. You cant expect him to behave like one. You don't seem to understand his character and why he is who he is. Male leads dont exist just to be these righteous honourable knights in shining armor. I hate cliche. And this is not cliche. Therefore I like it.
You also cant expect the people from their world to have our aspects in life. Dont forget what happened in the past of humanity. Stories like this tend to have inspiration from who we humans used to be. More tham what we are now. In the past if you had weird eye color theyd burn you for being a witch. That was reality then.
But this is fiction
I'm not expecting him to be all chivalrous; Naofumi from shield hero also has a lot of trauma he's working through, it clearly affects his actions, and is an amazing character! But he doesn't just stab someone because they made his wifu slightly miffed. And when he does something awful, the show makes it very clear that it's not healthy or encouraged.
But here, when Travis nearly kills someone for even annoying the FL, he's somehow "protecting his love" and it's framed as either a fluffy good thing or just a kind of side sweep. I'm not giving him a pass to torture people just because I think the main couple look cute together and he's got standard tragic past #276. The story should at least address it as a serious problem. Like the FL still being slightly afraid of him because of their first encounter, that was good! And he's actively trying to change his behavior around her to make her feel comfortable. Also good. However, the story doesn't seem to have a problem when Travis does even worse things to the other servants. He hasn't really changed, just became obsessed with the FL.
There comes a point when a person is really not mentally stable and should be seeking counseling and focusing on working through their issue instead of romance- see 50 shades of Grey. This perpetuates the equally annoying and far more dangerous cliche that you can "fix" or "change" a person of you just love them enough. Everyone is going to have baggage, but if your baggage causes you to STAB one of your closest allies, romance is going to make things worse.
Manga, if you're going to make Travis objectively outright abusive to his staff, don't frame him as the misunderstood lover who just needs to cuddle! This is seriously unhealthy. He's leaning toward yandere level, probably has already, but you're treating him like a normal male lead. This is like Harley x Joker. It's sad that to snap out of the "aww he cares about her" bubble, I have to say out loud "he stabbed one of his most long standing and loyal staff for mildly scolding the FL." Are we officially in reader Stockholm Syndrome yet?