Okay Galt here's the opinion of Harry Blackmun on Roe v Wade;<quoted text>
Abortion mentioned in the Constitution?
Homosexual marriage mentioned in the Constitution?
State criminal abortion laws that except from criminality only life-saving procedures on the motherís behalf, and that do not take into consideration the stage of pregnancy and other interests, are unconstitutional for violating the Due Process Clause of the Fourteenth Amendment.
The Due Process Clause protects the right to privacy, including a womanís right to terminate her pregnancy, against state action.
So there's your constitutional justification.
As for same sex marriage the crux of the matter is the 14th Amendment that guarantees all citizens enjoy equal rights and protections under the law. Since marriage is by its very nature a civil legal contract that gives both legal obligations and advantages then to deny it to working, taxpaying citizens because of their sexual orientation is unconstitutional.
As for either abortion or marriage being specifically mentioned in the Constitution, they're covered under the 9th Amendment;
The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people.