First things first, don't worry about English not being your first language. It's not ours either and it doesn't really matter in the big scheme of things - you can write good stories without knowing a bunch of complicated vocab or if you keep messing up grammatically or make spelling errors. Don't let that discourage you in any way, okay? We've been there, we've done that and we still mess up with a lot of "simple" things and people still enjoy the technical aspect of our writing. Besides, language is an art form in itself, so have fun with the sentence structure, use idioms/phrases from your native language and translate them into English and use them as elements to spice up your writing. The sky's the limit so just have fun and don’t worry about being perfect - and it’s something you worry about a lot, you can always try to find a native speaking beta reader if need be.

Anyhows, you seem to have three main problems, so we'll just split them up into sections to make it easier to break down and try to give you some advice💖

Endings: Will always be difficult and not everyone will ever be satisfied with whatever ending you create, so throw away those expectations and stick to what will do your story justice and not what someone else might expect. The main thing about an ending is that it’s a conclusion / a solution to a problem presented in the story so you need to know what the issue in the story is - what is the driving force of the plot/characters + what transpires to kickstart the action. When you know all of that, and you’ve written the story and reached the end and that’s what you need to write now then you can choose to highlight what has changed + how the characters have evolved (In FTN, we’re currently reaching the end of Mimo’s character arc and you will note that he spends a lot of time musing how he’s changed, or he will showcase through his actions that he had reached his full transformation.)

If you struggle a lot with endings, then try starting to envision the ending while starting out the story: Where do you want your characters to end up? Why is the story happening? What will change for them to be able to reach the climax of the story? Think of the ending, or the ending scene, before you even start writing so all the heavy lifting you need to do is to bring the plot/characters to that specific scene (In Apple, we knew we wanted them to kiss in the snow after Jeongin had reconnected with his brother again and we wanted to show that Hyunjin was willing to be a part of the church by extension of Jeongin.)

Also, in the end, the story continues off the pages anyways when the characters go out to live their life, so don’t stress too much about ending things properly. If your right ending is them kissing on the beach and having a moment of togetherness before facing the world again, then that’s the perfect ending for your story.

Plot holes/Consistency: Be neurotic and question yourself constantly: Why is this happening? Why is A acting like this? When did B decide to do this? How did they start feeling like this? What happened earlier in their life to make them act like this? Always question yourself and you’ll quickly discover all of the plot holes you’ve created - when it comes to plot holes in the world building, then just start thinking if you can invent something that solves this issue and then play it off as being such an ingrained part of this character’s world view that they just haven’t thought about it before.

Consistency - in regards to plot - is something you have to practice. Read what others do and how they progress their stories and learn from them. Try reading about plot structure models and learn from that, watch movies and see what they do and slowly you’ll be able to figure out when/where/how to do it and make the story flow seamlessly. It’s not easy and it takes practice and even now, after years of having written A LOT, we still make pacing mistakes or mess up the continuity. It happens and you can learn from every single mistake you make so while it sucks, don’t be too discouraged by it. It just means you’re progressing and is able to pick up on those flaws quicker.

World building: Realism is key even if you’re dealing with magic and werewolves. Think about how humans are shaped by their environments and figure out how the world has changed and formed the characters you’re writing about. Think about if a species has a specific way of greeting - like witches in FTN and ‘well met’ - then stick to it and for the love of everything holy, don’t explain it to the reader. Readers will figure it out really quickly that this is a witch thing and therefore you don’t need to coddle them. It’s the same with things that are natural to us - you wouldn’t ever explain to someone why you brush your hair in the morning because you expect everyone to be on the same page as to why that action happens. It’s the same with world building, everything that happens there is normal to the people living in the world unless something is terribly wrong (FTN Mimo explaining to the reader directly why it’s bad that he drips magic). Treat the world you’re building as if it’s real to the people living in it,

One thing of mention with world building - it is really important to remember the rules you create. If cats are considered godly beings, then don’t forget about it and make someone kick a cat later on without suffering the consequences of doing that or without making this character raised above the cat gods. Remember the rules and abide by them because otherwise all of your hard work is for naught.

The world has rules, we have habits and small quirks. To make a world realistic, you need all these. When you have a magic world, that magic will act a certain way, when you have divine beings, well, they will have their own way of speaking, of viewing the world. All of it matters, even small details so it’s important to make it happen all the time. In a world with gods, you will pray, in a world with magic you use it and you fear it. There will always be power balances, so make sure you hint at it even if your character is on the ‘powerful’ side. Worldbuilding is details, so don't shy away from them.

Hope this helps💖