The nature of a marriage is not determined by the Constitution, but by the laws of the state under which it is formed. However, the Equal Protection Clause of the 14th amendment might be successfully applied to strike down a law that has an adverse impact on members of minority class, if the state can show no legitimate interest that outweighs the disparate impact.
I don't think you can. You either has to be single or married to adopt. Just living together is neither. if you are in a samesex relationship and has gone through partnership might be possible though.
Anyone can do anything they want to as long as they truly want it. No, in Islam having a boyfriend/girlfriend type of relationship is not allowed whether your a male or a female and whether the bf/gf is Muslim or not. If you have anymore questions regarding the matter, just ask and I'll be happy to answer them. i gree in islam having a boyfrnd or a grlfrnd is not allowd but today no youngr generation follows it .....so if a muslim girl personlly like a non muslim boy...then it is not allowd in islam.....u cannot marry him unless he accpts islam...:)