If ...
1. Space is infinite; and
2. There is any other life out there whatsoever ....
Then ...
There are not only aliens, but there are aliens who look like us, one of whom looks like you, and has your family, and is probably having what you are having for dinner.
Why?
Because if there is one form of life, then there are an infinite (not just lots, but INFINITE) number of opportunities for a variation in the life form. An infinite number will be less like humans. An infinite number will be more like humans. Of those infinite number who are more like humans, there will be an infinite number of variations, an infinite number of which will be more like you.
This multiplication will continue for ever, and ever, and ever. The process will not stop until it reaches you !! somewhere out there.
And ... if that version of you is different fro the real you in any way whatsoever, there will be another infinite number of variations even further away which will eliminate those small variations.
Why is this concept hard to accept? Because our minds can't readily accept just what infinity means. We can cope with very, very, very big, like the known Universe, but we struggle a bit with infinity.
So the answer is yes, there must be aliens, and several of them must be calld loni2008, and quite a lot of them are looking at their computers right now reading this reply.