Hello, I'm Thomas Tergel. I only sell additional chapters to people who have bought previous works and that I can trust not to put on pirated sites. Each chapter takes between 4-6 months to create. It's disheartening to make literally no money on these and to see sites that have downloaded them by the thousands.
First of all you make great work. Let me compliment you on that and the fact that these kind of thought out stories are pretty rare.
However it seems to me you are misunderstanding the business model and market that you find yourself in. Creating this content is probably mostly a hobby for you which is good, but making money of it simultaneously is definitely possible.
There are a few aspects:
* People support work that they believe in or love. You create something that is extremely unique with lots of people who love it.
* People who don't pay for this content and post it on public fora's still attribute to your marketing, spreading your name and spreading your content to new geographies.
I can understand it feels painful seeing a lot of people consume this content for free, but all you need is to adjust to that fact and embrace it, make it work in your favor.
One way would be to create a patreon page (or something similar, lots of sites out there) then let people decide their own contribution (with differing tiers), don't be too greedy since a lot of the (English speaking) world doesn't have $20 bucks to spare for a single comic. Some people can literally live a week from that. Basically you are losing people who would donate between 1 and 10 bucks, which is definitely the majority.
But besides that you make money by offering people "early access" to your comics. The higher the tier, the more exclusive, better and earlier they get their content. Furthermore you can offer behind the scenes, or extra images which tend to not leak out as much as your main comics. People love that and you will soon find many supporters. Especially if you build up a lot of anticipation for the next comics, releasing your comic a week earlier then releasing it yourself to the public (uploading to f95 and/or exhentai) will be more than enough incentive for people to subscribe, this is a fact you can check on many other channels. Publicly releasing your own content is also highly recommended because of the (quality) control, consistency and generating an audience for these public channels (which you can later monetize).
There are more creative ideas, for example studio fow (In their earlier days) had this mascot (girl) that would talk and chat with people. People were supporting and paying just for that. Not saying you have to do the same, but I just want to show that there are many options to monetize. One last: make people vote with money on future content.
You really have gold in your hands my friend. Just think how to capitalize on it.
The bottom line here is that if you start resisting the market (trying to hide your content behind very strict paywalls or personal authentication), you are mostly hurting yourself. Don't fight the flow, it will only cost you.
One more small tip: Spread you work in smaller chapters (20-40 pages each). Having consistency and regularity is much better for monetization, spreading your name and people supporting you, very few people would pay for a patreon that releases once every 6 months, the expected time per release is about a month or less from consumers.