[M4m/f] Your boyfriend's older brother shows you what a real man is like

You've known my brother for years; it took him that long to build up the courage to ask you out. He's sweet, caring, a bit of a pushover, especially to me. I left for college while you two young sweethearts continued your relationship.

One night when I'm home visiting and he snuck you into the house after our parents went to bed, we meet each other after lights out either going to the bathroom, or getting some water, and by the time you realized I was naked, you also noticed I was much more endowed than my little bro...

Can be slowburn or just straight to smut.