I bet you lend out $100 bucks all the time and never expect it back, right? It's a $100 bucks. Plus, he said he'd pay me back promptly - my feathers aren't ruffled over the money really, although to me it is a lot of coin. It's just that he said he'd pay me back and he hasn't for 3 months. If you don't want to pay me back, fine, but don't say you will and then don't - had you told me you wouldn't pay me back the $100 bucks I wouldn't have lent it to you in the first place.
If it's that big of a deal to you, then demand payment and ruin your friendship. Plus if you didn't have a notary around while you signed the contract, there's nothing you can do but bitch about it which is pointless to do in the first place.
Lesson Learned: Don't lend money to friends and family that you expect to get back.