Well, it's estimated that there are 100,000,000,000,000,000,000,000 stars in the universe, and it's also estimated that most stars have at least one, if not more planets, so the number of planets is around 10,000,000,000,000,000,000,000. The chances of only one of those planets sustaining life would mean that there would have to be .0000000000000000000001% possibility of any one planet at any time sustaining life, and of course that number is no where near the actual estimate for planets that actually have the right conditions to sustain life. Out of the 50,000,000,000 planets in our own galaxy, around 500,000,000 are thought to be able to sustain life in the habitable zone. There are more than 100,000,000,000 galaxies in the universe. Do a bit of math and you get 50,000,000,000,000,000,000 planets that are capable of sustaining life, give or take a power of ten. There's a less than 1% chance of most planets that are in the habitable zone to sustain life, though that number increases and decreases based on the size and other factors pertaining the planet. There's no question about life not existing out there, just whether or not it has evolved to the same extent that we have, and I'm sure it has somewhere.
To find the probability of life existing on other planets, you need to take into consideration a huge variety of things. Most estimates fail to take into consideration a lot of things such as living conditions that might not be suitable for the average Earth born organism. A lot of new discoveries point towards the possibility that there are new suitable living conditions that we haven't thought of as possible for sustaining life before. Earth is also a relatively small planet, and the main factor regarding the probably of life existing is the habitability of a planet. Things like planet size, gravity, the sun's life time, the planet's life time, the number of moons, meteorite belts, nearby planets, etc. all factor into the result, and astronomers haven't yet gotten a good enough picture for most of these, so estimates are usually off.
We've barely even started looking for life. It would be extremely, extremely unlikely and absurd that we would find life in the few years that we have looked for it. Even so, there's a probability of life existing in our own solar system. There's evidence of water to have existed on Mars recently, and 4 moons of Jupiter and Saturn are believe to be able to support life bellow the surface in an underground ocean. In our own galaxy.
We are made of the most abundant elements in the entire universe. If you rank the elements that we are made up from most to least you'll see that they match the abundant elements in the universe exactly. It's not only us that exist in the universe, it's the universe that exists in us. We are all made of the same things. We are not special in any way and to say that we are the only living things in the entire universe is extremely egocentric and naive. The right conditions and materials to make life exist quite abundely when you take the size of the entire universe into consideration.
I still find it a bit mindblowing to think that there's a chance of things existing out there that might be living a life similar to things on this earth, or even to us. It's a pretty amazing feeling isn't it? A sort of belonging.