Is trigeminal neuralgia in young adults always a sign of impending ms? I'm 28 and have had tn for a little over 2 years.

No, The neuralgias, or nerve pains are among the common MS symptoms. One of these is trigeminal neuralgia which causes severe electrical shock-like pain. TN rarely occurs bilaterally; when it does, it is usually secondary to multiple sclerosis.
No. Young people with tn, especially bilateral tn, should be evaluated for ms. However, recognition of tn is increasing, and finding tn in young adults, even teenagers, is on the rise. The reason is unclear. For the most part, the causes seem similar to that seen in older adults, and the approach to treatment is similar (first medication, and if that fails, procedure).
Not necessarily. Trigeminal neuralgia rarely affects your age group and it doesn't necessarily mean you have multiple sclerosis. Consult a neurologist or a orofacial pain dentist for a second opinion.
Not necessarily. Trigeminal neuralgia can be associated with nerve irritation at the base of the brain, and can be seen with blood vessel compression, neuroma presence, contact against a bony surface within the cranium, and associated with any disorder than can impair cranial nerves. Although there is an association with ms, has a spinal tap confirmed ms? Get a high quality MRI with a neuro-radiologist.