As you stated, we've explored our Universe, alone, yes, but there are a few questions to ask, if there are other civilizations, what if they're further than our current reach? Or maybe they're more advanced that us and have mastered cloaking technologies? (we're a bit close to that ourselves) Or maybe there are civilizations far away that have achieved only the same or less progress as humans and they've yet to explore outside of their solar system? There are a lot of questions, and I personally wouldn't believe an extra terrestrial life form exists without seeing it for myself, but hey, it's your beliefs, if there's but one thing free in this world, it's beliefs.