Hi there!
This is a simple twist on an old thought, designed to shake people out of complacency about the nature of God. The thought is typically "I know who God is, I know what He is, but does He really exist?" This is arrogance. First you are assuming all sorts of information about God, who you later go on to question, then you are questioning Him, as if all the stuff you thought about Him is irrelevant.
Either be objective and do not attribute anything to God in the first place, or find another way to question Him. I have suggested the latter, another way to question Him. This way is to simply say "I take for granted all that I do about God, who He is, where He is, what He does, but now because I am human and compelled to doubt, from time to time, I will question why God is not different to all that I have taken for granted about Him? I will ask why am I not fundamentally wrong about all I have assumed can be attributed to God, if I must be wrong about anything?" This is healthy doubt, because it can be answered by the exercise of the will, more generally, and not just the intellect, as is the case with the question of the existence of God.
Once you have determined for yourself, in the absence of needless distractions about whether someone else thinks what you do, why what you know does not change, you will see that the question about whether God exists is actually a much more circumstantial question than you might first expect. Questioning whether God exists, hinges on the self-importance of the questioner being able to renounce God's Godness as if that is somehow the choice of the questioner and not the choice of God.
There are many things you know about God, all of them come from Heaven, if they are from Him. They tell you about what to expect of God, what His nature is, how His imagination works, these are important learnings, they are not to be neglected. If you can keep from mixing these things with the opinions of others, but trust that the God within you is able to reveal the truth to you that there is about his nature and the nature of His love for you, you will find that it is actually very easy to trust Him whether or not He exists...
...that actually, whether God exists or not is the last thing on your mind.