Do you recall when you stopped being a “doubting Thomas”? At what point did you truly believe that Jesus was your savior? It is sometimes hard to move beyond that point of faith and believe, to knowing and having surety that God is there for you.
We know He is, but sometimes, the devil is an expert in running interference in our lives. He wants us to doubt, to move away, to not stay close to Him. As the Psalm says:
For steadfast is his kindness for us,
and the fidelity of the LORD endures forever.