Since you do let the cat roam, the problem may solve itself fairly soon. Indoor-outdoor cats have a greatly reduced life expectancy. 
But if you insist on letting him roam, you might consider a cat door. Then he could come and go as he pleases, and reward you by bringing you “treats”.
Sorry to hear the cat is causing nighttime disturbances. My folks went through the same thing with one of their cats. He cried all night and paced and cried all day. It turns out he was suffering from hyperthyroidism. It causes restlesness and agitation. Now he’s on meds and sleeps through the night. (My own cat is also being treated for it) He just cries now for food, constantly.
It’s just a thought. You may want to get him checked out to make sure there is not a medical reason for his incessant crying.
BTW, hyperthyroidism is very common in cats.
http://www.vetinfo4cats.com/chyperthyroid.html#Hyperthyroidism%20in%20older%20cats
Yeah, but what he’s describing sounds like a perfectly normal,healthy Siamese, really. All cats are primarily nocturnal and alternate between short periods of sleep and activity, just as he describes. And a good rule of thumb for a Siamese is that if its eyes are open, its mouth is going to be open. They talk. They talk a lot. They talk so much that I’ve had people call and say they know the cat is sick because it’s not meowing constantly.
It never hurts to get them checked, but I don’t think I’d bother in this situation. If the cat started losing weight or having hair coat issues, yeah, but not because he’s awake and talking all night.
No kidding. And exactly who pays for the house in which your room is contained? Perhaps, if the cat, or rather your mom’s reaction to him, is such a problem, getting your own place would be a great way to get the sleep you need.
Heh. I’ve lived with Siamese cats a good part of my life, and ALL of them talk(ed). My current meezer girl likes to talk, but she is, for a Siamese, relatively quiet, which amazes my daughter, who frequently wonders what a “normally loud” Siamese sounds like.
Sapphire hates to be shut out of the bedroom, or bathroom, or ANY room. A closed door is an affront to her. We keep her inside, despite her wishes, but otherwise, she’s allowed to go anywhere in the house, except for certain circumstances…for instance, she was shut in the back half of the house Halloween evening and night, so that she wouldn’t get out while we were constantly opening the door. She gets shut into a room when we bring in groceries, and have the door open. And she gets shut away while we have repair people come to the house, because she will usually try to seduce them or assist them or both. In particular, she does not like to be separated from ME, because I’m her person.
Maybe Buster (which is a great name for a male Siamese, by the way) would be somewhat less vocal if he could come and go into your bedrooms at will. I know that Sapphire loves to curl up on me when I go to bed. And a cat door might help…Siamese are quick to learn behaviors that will get them what they want.