Meaning being and performing all the actions of a significant other?
Let me restate your question, so that we understand one another. Can an 18 year old person and a 16 year old person legally have sex? Yes. The "age of consent" is 16 years old in Michigan. That means that a 16 year old has the legal ability to consent to sex. Is it smart is another question. I would encourage you to find an adult mentor(not a classmate or a youthful adult friend) to discuss this with . You can always delay things that you cannot "undo."
There are circumstances where this would be illegal as well. Amoung others, this type of relationship would be illegal if the older person is in a position of authority relative to the 16-year-old or if there is an allegation that the 16-year-old is under the influence of alcohol or other controlled substance. Sexting and illicit photographs would be illegal as well. This type of relationship is ripe for all kinds of problems.
Make sure the 16 year old is, in fact, 16 years of age, which is the age of consent for sexual activity. Make sure that the 16 year old does not have any mental deficiencies which could translate into the 16 year old having a mental state equivalent to that, let's say, of a 10 year old, because that could present problems.
Neil M. Colman
Mr. Colman is licensed to practice law in Michigan. The response herein is not legal advice and does not create an attorney/client relationship. The response is in the form of legal education and is intended to provide general information about the matter within the question. Oftentimes the question does not include significant and important facts and timelines that, if known, could significantly change the reply and make it unsuitable. Mr. Colman strongly advises the questioner to confer with an attorney in your state in order to ensure proper advice is received.