You are one of the most reliable people I know.
'Affidabili' = af-fi-DA-bi-li, stress on third syllable. 'Conosca' = co-NOS-ca — subjunctive.
Use this to express deep trust and respect for someone's reliability. In Italian culture, being reliable ('affidabile') is a serious character virtue. This compliment shows you have observed their character over time and value it greatly.
'Conosca' is the congiuntivo presente (subjunctive) of 'conoscere' — used here because of the superlative + 'che' structure. Italians use the subjunctive after superlative expressions: 'la persona più brava che conosca' (the most skilled person I know).
Mi fido di te ciecamente.
I trust you blindly.
'Ciecamente' (blindly) — complete, unconditional trust
Quando dici che fai una cosa, la fai.
When you say you will do something, you do it.
Describing the specific behaviour that earns the trust
Con te non ho mai dubbi.
With you I never have doubts.
Absence of uncertainty as the measure of trust
In Italian culture, keeping your word ('mantenere la parola') is a fundamental mark of character. The expression 'una persona di parola' (a person of their word) is one of the highest compliments. Conversely, 'non è una persona di parola' (he/she is not a person of their word) is a severe character judgment.