Having a scent of a chemical on the breath or clothing is, unfortunately, a definite sign of inhalant use. (I'm not saying that your boyfriend is, but the chemical odor is certainly a warning sign.) My friend actually has a severe BRAIN INJURY from huffing at the age of 12, now in her 30s.
Please TELL his mom or dad, if even anonymously, since a person can DIE or get permanent NEUROLOGICAL (brain, spinal cord, nerves) damage even after the very FIRST time of use.
For more general info re: (regarding) the dangers of huffing - National Inhalant Prevention Coalition: http://www.inhalants.org
A support group for the friends (such as yourself) and family of the addict is Al-Anon, and one may attend an "open" meeting if the loved one doesn't have a drinking problem: http://www.al-anon.alateen.org
Please go with your "gut feeling" - that inner voice that tells us that something is just not right. Hoping that your boyfriend (and yourself) makes good, HEALTHY choices in life.