I Have One Back Tooth That is Loose. I Suspect Bone Disease. If I Have It Removed, Will my Other Teeth Space Out? If So How Soon

If you have incresing mobility with this molar there is a good chance that it will need to be extrated, but it should not cause any spacing of the other teeth.  I would see your general dentist first, allow them to examine the tooth, then see a periodontist if they feel that is necessary.  A 3D CT scan of that area will determine quanity of bone, whether an extraction is nessecary, and whether or not it could be replaced with a dental implant.  Hope this helps.

Once you remove the loose 2nd molar, it'll take years and years for your 1st molars to drift back.  I wouldn't even worry about your front bottom teeth spread apart because they won't.  If you lost all of your molars on one side, then yes, your premolars and front bottom teeth may also spread and drift.  Since you'll have your 1st molar left still, you'll be fine.  NOW, this is all assuming that you have NO gum disease.  Yes, go see your dentist and make sure your periodontitis is under control.  if you periodontitis is NOT under control, not only all of your teeth will drift, but you also chance loosing more teeth due to mobility.

If your tooth is loose then it might be a goner.  Honestly, it's going to move through just normal eating, thus even with periodontal therapy it might not be able to 'tighten up'.    That being said, IMO , it's only a matter of time until tooth needs to be extracted.  Especially if you're noticing increasing spacing. 

Yes, I would recommend you see a periodontist to see if there is still something that can be done to keep your loose tooth.If your tooth is loose because of gum (and bone) disease, then at some point your dentist will usually recommend it be removed.  It is better to remove it earlier than later, as the longer it goes, the more the bone will be lost as well.And yes, after removing a tooth it should be replaced by either a fixed dental bridge, a dental implant or a removable partial denture.  If not, the tooth that opposed the missing tooth will start to migrate into that space, and the teeth on either side of the missing tooth will drift into that space.  Thus, throwing off your entire bite.This whole scenario takes a while, usually a few years to become noticeable, so better to make the corrections within the first year of losing the tooth.

Generally I tell my patients in this situation that if they want to do everything they can to keep their teeth they should see a specialist.  It is impossible to diagnose your situation without seeing you.  Having said that,  I sounds like you will be loosing the second molar and possibly more teeth.  Your first priority is getting the disease under control and focus on the teeth you can save while getting rid of those you can't. Once this is done a thorough evaluation of your bite and what it will take to stabilize it is needed.  When we loose posterior teeth is can cause opposing teeth to supra erupt, adjacent teeth to drift, and/or a posterior collapse of the bite.  This collapse places inordinate amounts of force and strain on the anterior teeth resulting in excessive wear, crowding, splaying of upper anteriors, fracturing etc etc... .  One thing to remember,  just because you don't have pain does not mean you can't have active periodontal disease.