I don't think it's relevant to decide whether you 'believe' or not - given the scale of the galaxy and universe, it's likely to be statistically certain there is other complex life out there.
None of that really matters if we never cross paths with it, and given our place in the galaxy I'd bet on us - at least - never seeing a trace of it from here until the Sun shreds our atmosphere and our species dwindles. Yes, I am just a [proverbial] ray of sunshine when it comes to life and the universe... ;-)
I find it fascinating to think that if we ever do develop means of escaping the Solar system and exploring the stars, it could be more probable we discover the remnants of intelligent life; ruins of a civilisation spread amongst a system or two, perhaps. There'd be no handshake or mutual exchange of ideas, but it would result in generations worth of incredibly hard to collect/extract/study xenoarchaeology (given the worlds we find the ruins on would likely be extremely irradiated and otherwise hostile to human existence), and we'd finally know we weren't alone - even if we still kinda would be...
(though if we developed means to escape the system, it's more than likely we'd have long had means to detect the remnants of the other species well before we venture out)