I'm always glad to see I'm not the only one (selfish as I am…) I've had long periods too when I've really struggled to keep writing. So demoralizing. The longer I went without getting anything done, the worse it got. I knew that there really was no other solution than to sit down and do it, and keep doing it, even when it felt impossible - but it could still be so very, very hard.
I don't have much to add to all the good advice here. Change your writing style from pantsing to plotting or vice versa to see if that helps, write scenes out of order etc etc. I just wanted to point out that each time you abandon a project you wanted to do without finishing it, you make the next one harder to finish. It's a neurological thing – when the process of starting a novel has happened 'so so many' times as you say, and each time it has never been brought to a conclusion – then your brain has been taught that this process
will not lead to a conclusion – there is no conclusion to be had, actually. So in a very real sense, it
is harder for you to bring this novel over the finishing line than it would have been if this was your first draft.
I don't mean to discourage you, quite the opposite. You're not only fighting the novel, which is a huge challenge in itself, you're also fighting your past experiences. Take that into account and then you can see how good you really are, how well you're actually doing when you keep going like you do. Each time you sit down and write, each time you get even a few sentences further in the draft, you've accomplished something big. Reward yourself for that, don't focus on how little you get done and how hopeless you are and how you will never finish. You're not, you're doing fine, and there's no way you won't get to the finishing line if you write even as little as one sentence per day. You
will make it. And you're right. The next novel will be a little easier, because now you've taught your brain that bringing this kind of project to a conclusion is actually possible.
I don't know if this kind of trick will help, but maybe it's worth a try: plan a smaller section, a scene, a chapter, that you can realistically finish in a few days, a week's time maybe. Open a new document for it, write it to the end and call it finished. Save it in a file called 'finished scenes' or something, then celebrate your achievement You can easily paste the scenes into the master draft later as you need them. This way, you are giving yourself the repeated experience of finishing a project you've started
that is related to the novel. And you can see the finished scenes adding up, even count them, to celbrate how good you are at finishing.
Yeah, like I said, a trick that may not help you at all. The main thing is to keep going and to
celebrate the fact that you are making progress in this uphill battle you're fighitng, instead of despairing. You're doing great.