Your friend may be sincere, but I'm afraid in this case he is sincerely mistaken, nor is there any evidence for what he apparently believes.
The reason is because Jesus made it very clear that His second coming would be glorious and visible to all humanity. He taught, "For as lightning that comes from the east is visible even in the west, so will be the coming of the Son of Man. ... They (the nations) will see the Son of Man coming on the clouds of the sky, with power and great glory" (Matthew 24:27,30). His first coming went almost unnoticed; His second coming will be glorious and seen by all.
When Jesus comes again, He will rule with power and authority over all the earth. He will come to judge evil, and to establish His rule of perfect justice and love. While the Bible doesn't answer all our questions, we should never forget that this present world system is only temporary, and that some day "the kingdom of the world has become the kingdom of our Lord and of his Christ, and he will reign for ever and ever" (Revelation 11:15).
Yes, some day Christ will come again. No, we don't know when–but until that time, make it your goal to live for Christ every day. Are you ready for His coming? If not, or if you aren't sure, make your decision for Christ today, before it is too late.