To understand how to communicate with the lease-holder, we need to better understand your relationship to them and so, we need to properly understand the exact scenario and what it means for each of you.
In Australia (and I will assume wherever you live), subletting a "room" to a new tenant means getting written consent from the owner, and they cannot reject for no reason. The lease-holder is allowed to set the terms for any room and sublease to as many people as he wants and adding more tenants would not change prior agreements (this means your amount does not get lowered when there is a new tenant added)... that is, so long as the owner keeps giving permission. But you see, if the number of tenants exceeds the original proposed amount in the lease or if the owner feels it might be overcrowded then the owner now has a valid reason to withhold consent for another tenant to be added and 90% of the time they will do just that.
So, 100% of this new guy's rent will go to the lease-holder and your original agreement/amount will be unchanged. The thing is, normally he would not be allowed to add another tenant because it so clearly devalues your room, not to mention the fact that the new tenant is renting a storage room or how it seems he ?maybe? has not received consent the owner to begin with. Remember you don't actually know this information, and its entirely possible the owner is fine with it. Just not common.
So, then we come to the discussion about renting out the storage room. OF COURSE the lease-holder will want to add another tenant, it means more money for him, and he has every right to do so as long as the owner agrees... I'm not so sure about the qualifications for a "room". Anyway, they did the very reasonable thing about asking the group if they were okay with it first. THIS was the time you should have spoken up. Adding the new tenant benefits the lease holder in every way, and you in none and its why you feel that its not "fair".
Basically you are in a bit of a pickle. You have set the situation up so that the lease holder has no reason to tell you what he will do with the money let alone split it. It is his money, that is just the way it is. If you complain about the new tenant then he will say he already asked everyone if it was okay and the consensus was yes. You can try to appeal to his emotions and explain how you were falsely under the impression that a new tenant was a shared benefit or some of your troubles about it being right outside your room. I would say this is your best bet for getting him to communicate if he continues refusing but I doubt it would help much with anything tangible. Basically the lease-holder is totally justified to just tell you NO, and if you react poorly then it will be you in the wrong, not them.
Now, your sublease's value has gone down slightly and you are still paying the original amount. Welcome to the club. You now have to make some decisions, will you live with it? Try to catch the lease-holder out on some violation? Move to a new place? I don't know, but the lease holder has actually been respectful to you thus far (even though it initially seemed otherwise) and they have the power, and you might have to live with them for a while, so whatever you do try to be calm and respectful when communicating with them. Also compromise is good.
