When alcohol is consumed it affects many parts of the brain.
Endorphins are released which attach to the opioid receptors in the brain and cause a chemical cascade that creates the compulsion to continue that we are unable to regulate - that is the part that the naltrexone blocks.
The pre-frontal part of the brain is also affected, which means that you will get relaxed and buzzed when alcohol hits it (that is what you are likely experiencing, just like normal drinkers after a couple of pints), and indeed gets intoxicated if it is overrun by alcohol i.e. you get drunk. The prefrontal cortex of the brain is also where the stop and go signals are produced.
So, with the chemical compulsion being blocked by the naltrexone, it gives you the ability back to make better decisions about your drinking. This is something quite new to many of us who begin naltrexone because we've generally never had any decision-making ability ever - when we drank, we mostly drank more than we intended and didn't know why!
The naltrexone is a partnership between you and it. Taken as intended, an hour before drinking, every time you drink and you will no longer receive that compulsive signal in your brain and you will have a choice. It will help you to make better decisions, so your part is to begin to learn how to make those better decisions as far as alcohol is concerned. And this is a key point - if you overload the prefrontal part of the brain with too much alcohol, or too quickly, you lose the ability to make the decision even if you want to.
A suggest might be to look around you in the pub. Many are drinking slowly, enjoying the social event and in good conversation or good food. That is usually what 'normal' drinker too, and you goal will be to slowly move yourself towards drinking how they drink. i.e. a normal drinker will (for the most part) decide to stop at a certain point of the buzzed feeling. They might switch to a coke, or maybe even a coffee. They generally don't keep drinking beyond that point.
Slow but sure, start to decide what type of drinker you want to be and then move towards it. If you are looking to be a moderate drinker, for example, then start learning to interrupt your drinking when your brain gives you the signal to do so..... and keep an ear out for that signal by not over loaded your brain with alcohol. The body processes alcohol at a rate of about 1 unit an hour, so if you drink more than that then you will end up overloading your brain with alcohol pretty quickly, and in turn rendering yourself incapable of acting on a decision.