How can a person support the repeal of DADT, but not support same- marriage?

Basically, you are saying that a gay person can fight for our country, put their lives on the line, and defend and fight for YOUR freedom, but what do they get in return? When they come back home, will they have equal rights? This was brought up at school today after some kid said he supported the repeal of DADT, but opposes same- marriage.