Notarization is irrelevant in this context: it neither adds nor detracts anything. If he gave you a deposit with an offer to buy your home, which offer you accepted, you are bound by your acceptance until and unless he violates one of his obligations. So, for example: say he gave you a $1,000 deposit, but had to come with either a larger down payment or the entire purchase price by a certain date; if he fails to do that, then you could terminate the agreement for his material noncompliance or breach and also keep the deposit. But if he's still complying with any of his obligations, hasn't exceeded any time frames, etc., you are still bound.