Your GP was following best practice, which is what ideally they're meant to do for every patient who goes on them. Requesting frequent reviews doesn't necessarily imply anything about the proposed length of treatment — usually, once they're happy you're settled on them and they're working, the reviews should become less frequent, though everyone's treatment will be different.
You're right, though, that usually, the initial assumption for somebody being treated for the first time is that this is not intended to be forever. The standard recommendation is that you continue antidepressant treatment for at least six months after you feel better, after which you can talk to the doctor about seeing how you do without them. Different circumstances might merit different action tho obviously.
Since your doctor seemed to be conscientious about making sure you were safe and monitoring how you were responding when you started the antidepressants, I'd hope she would be equally good at helping you safely and comfortably stop the antidepressants when you decide to do so.
Ideally, finding the right antidepressant treatment is supposed to be a rational, planned process, where you feel you have a handle on what's going to happen at each stage and in the future. It shouldn't just feel like desperately increasing and increasing something that's not helping because you've no other option.
What's meant to happen is that they start an antidepressant either at the lowest effective dose, or building you up to the lowest effective dose. Then you wait for a few weeks/months, to see if that does the job. If it does, stay at that dose. If not, increase to the next step up, and same again. Maybe increase again if it still seems possible this drug may be effective at a higher dose.
If it feels like it's not even helping slightly at lower doses, or you've tried the maximum dose, or it's otherwise clear that it's not going to work — or you get a side effect you can't tolerate — you can start again with a different drug, or sometimes if it's partially working you can add another drug, though that's less likely. Or you can try other treatments without medication.
Sometimes people experience what you did, which is that the drug seems to work for a while, then stops. I know some people for whom that meant "right drug, too low a dose", some people for whom these poop-outs only happen after many years in a particular drug/dose, and very occasionally the odd person whose body seems to just get so responding to whatever drug at whatever dose after a fairly short while. The GP should still be able to respond to these with a plan of action that makes sense to you.
If you get a drug and a dose that's working, you stabilise on it for a while, then when the time seems right you can choose to see how you do without it. Again, this should be a planned, rational process, with explanations of what to do if you experience any withdrawal effects and how to manage them if you do, and what to do if your original symptoms come back, whether soon after or much later.
It seems like your family members maybe haven't had as much support as they ideally would've, with starting and stopping, maybe haven't been given an explanation of the plan of action, or their doctors are flying by the seat of their pants and being reactive, or they can't get the appointment time they need to sit down and put together a plan with the doctor that follows the guidelines, or they have complex, long-running mental health problems that perhaps aren't exactly the same as what you're dealing with. It's not supposed to feel that way, like ever-ramping doses then being left alone to deal with the consequences — I guess too often, because of lack of time and resources, it comes out that way, but your GP sounds pretty good, so I hope that they will be helpful, whether you decide to stick with this dose, increase it, come off them altogether, switch drugs, or whatever you decide.
BTW I get my ferrous fumarate really cheaply from Amazon or eBay — it's perfectly decent quality, and because I tolerate it fine I don't see any point in spending a fortune on health shop stuff 