Why the center of our galaxy doesn't absorb us?
The spiral arms don't mean that the mass is getting sucked to the center. They're just wave-like density patterns.
The bodies in orbit around the center of the galaxy are in stable orbit; just like the Earth around the Sun and the Moon around the Earth. What happens is that gravity accounts for the centripetal force (in the orbiting frame, gravity is balanced by the centrifugal force), so there is no net radial acceleration "left over" to suck the body in.
The only reason things would fall into the center is if they were headed there. This can happen if two stars pass by each other and are slingshotted in opposite directions, one of which gets sent to the center of the galaxy.
To the original poster: You appear to be operating under the "hollywood" misconception that a black hole somehow "sucks harder" than the same amount of mass in a non-black-hole form. However, this false "black holes produce an enormous sucking" misconception is one of the many, many concepts of physics that "hollywood" gets totally wrong; a black hole of a given mass produces exactly as strong a gravity field as an object made of "normal matter" having the same mass. If, for example, the Sun were somehow instantaneously replaced with a 1 solar-mass black hole, the orbits of all the planets in the solar system would remain unchanged in the slightest, and the only way anyone would know anything had happened would be that "the Sun suddenly went dark."
Nor despite superficial appearances is the galaxy a "bathtub vortex" draining down the central supermassive black hole; as other posters have noted, the spiral arms are not "streams of matter," but rather concentrations of bright, hot, short-lived stars that form in the wake of "density waves" propagating through the gas and dust of the galactic disk.
Thus, as other posters have noted,stars do not "fall into" the central supermassive BH for the same reason that the the planets do not "fall into" the Sun: They are in stable orbits around the galaxy.
Moreover, please also note that the mass of the central black hole in a spiral galaxy is minuscule compared to the mass of the galaxy itself --- only a small fraction of a percent --- albeit that mass does appear to be correlated with the mass of the host galaxy, see e.g. http://iopscience.iop.org/0004-637X/737/2/50/. (Why the mass of every supermassive BH appears to be about the same small fraction of a percent of the total mass of its host galaxy is still an open question.)
The super massive black hole is creating a force acting on the material in the galaxy, but that material still has angular momentum which needs to be conserved. In a similar way, the earth is in orbit around the sun and it is bound in its orbit by the gravitational potential from the sun's mass. If you were to naively calculate the force on the earth as $F= G m_\text{earth}M_\text{sun}/r^2$ you would conclude that the force would pull the earth in, however you would have neglected the angular momentum of the earth, for it to fall in it would need to lose its angular momentum (L) . Since $L=m_\text{earth} v\times d $, where d is the distance to the sun, this means the earth would need to decrease its orbital velocity to decrease L.