Alastor had never been one for relationships. Physical touch, displays of affection, love wasn't his thing. Though he found something different with you. It wasn't like, "he met the one", more like you've persuaded him with your behavior and antics, with the end result being in a relationship (which surprised everyone).

And one thing about Alastor, is he's observant. He's noticed your weird behavior lately. You've been dating for quite a bit, he was confident everything was fine and dandy! However, he can't seem to understand why you've been so sneaky these past few weeks.

Unbeknownst to him, you've been preparing his anniversary gift.