Firstly, you need to sit down and really analyse what you're feeling. Is there something in common with all the times you lose interest? Does it always happen around the same time, or for the same reasons, etc.? If it's that you get distracted by a new idea, it might be worth trying to figure out how to either a.) put the new idea on hold while you finish the old one (and still be excited because now you have something to look forward to!) or b.) do both at the same time, if you have the time for it.
Questions to ask yourself: Are you growing bored because you haven't got any idea where you're going with your story? As in, you haven't planned enough? Are you getting bored because you've planned TOO much? Are you getting bored because you're trying to make things people want to read rather than stuff YOU want to tell? Are you getting too hung up on what people might think of your story? Have you really figured out WHY you want to tell your story?
Read a lot of comics. Read a LOT of comics. And I don't just mean read them the way a regular reader would; find pages that you like, and pick them apart. Why do you like it so much? How are the panels laid out? How to the speechbubbles flow across the page? What is it that makes the font look good? Etc. Learn by analysing what other people have done well. And, conversely, find stuff you DON'T like, and figure out why it DOESN'T work.
It's how I've learned what I know about comics.
And secondly - it's okay to not want to do comics. It is. It's okay if comics aren't your storytelling medium. There are LOADS of ways to share stories that aren't comics. You can do illustrated stories - i.e: prose with the occasional illustration. You can just do straight up illustration - there are ways to pack a lot of story even into a single image. If you want to do a longer narrative there, you can just do a series of illustrations that go together, but which aren't comic pages.
It is 100% okay for comics to not be a good fit for you. I used to think I'd grow up to be a novelist, until I realised that long-form prose wasn't my medium - comics were. I've got, like, 10 unfinished novels kicking around. That's hundreds and hundreds of thousands of words I had to wirte before I figured it out.
ETA:
It does seem like you have issues finishing anything at all, and not just comics. This could be a symptom of a LOT of things, and I'm not going to psycho-analyse you, because I don't have the necessary knowledge for that - but have you tried doing short, oneshot things? Like, 30 pages or less for the entire story, beginning to end? Not chapter one - the whole thing.
Sometimes, we have to practise finishing stuff.
I left a mess of unfinished projects behind me before I started doing shorter oneshot comics. It takes practise to learn how to structure a project, how to carry it out, and most of all it's worth learning how it feels to finish a thing, write "The end", and put it away. And you can start on as small a scale as you want, and build up from there.