This seems rather sudden. My cousin didn't force you into this, did she? Please remain calm and rational, and remember that long-term commitments require long-term mental preparation and significant decision-making time. As far as I am aware, engagements can last a few decades if you need the time to consider it further before settling on definite plans, and above all, don't make any decisions or promises when you're happy! It introduces significant bias into the equation.
I'm here to help, when you need it (and you most certainly will),