Let's start with "I'm coming out" from under the rock you've been living under... ;) When a person says he or she is "coming out," it usually means being straightforward about his or her sexuality (gay, bisexual, etc.). Further, since homosexuals are technically not allowed to get married in most states, their significant others are referred to as "domestic partners." But usually only on paper. I know gay couples that refer to each other as husbands.
In Oregon State - since February 2008 ( supreme court, fought of John McCain / Arizona State from blocking the Marriage for just about anybody... judge threw it out. 'An Outsider, who doesn't live in the State can't be grounds for holding up Civil Rights of others to get Unions, and Benefits.)
domestic partner usuallymeans ur a homosexual who is living together and/or has had a sortof 'wedding' ceremony. Coming out means ur letting everyone know ur gay or lesbian rather than continuing to hide it
Domestic partner means someone you live with, romantically usually. I'm coming out could refer to coming out of the metaphorical closet, as in going public with your gay bi or transgendered sexual orientation.