What are the principal beliefs of Sikhism?

My understanding is that they believe there is one God. My boyfriend told me they believe in many.

Try http://www.religionfacts.com/

My understanding is that you need to take a seat over there.

Ok Me. The basic beliefs of Sikhs are.

There is one God.
He is formless.
He has no Gender.
They believe in Equal Gender Rights.
Human rights.
Respect all other faiths.
Treat everyone the way you want to be treated.

Your Boyfriend is confusing Sikhs with Hindus.
Hindus have Load of gods for all sorts of reasons.