A clear no is kinder than a maybe that drags on for three weeks.

A maybe that never resolves costs the other person more than a no would. They hold the slot open, turn down other plans, check in twice and feel awkward about asking a third time, all for an answer you have had for three weeks. Dragging it out is usually about sparing yourself one small uncomfortable moment.

Give the answer you already know today, by message if that is easier. Keep it short and resist padding it with reasons that invite negotiation. Most people are relieved to be let go, and they will ask you again next time.