Dear Future Sister-In-Law,
Let me start by saying welcome. Welcome to the family! Now just so you know, you are the woman in his life, but my mom and I still take precedence. I'm sorry, that's just how it works! I'm kidding... But, also not really. I hope you're prepared to enter this family... We are fun, exciting, loving, caring, crazy at times (not like "wow stay away from them" crazy, but like "ha ha ha did they really just say that out loud at a family function" crazy). We will do anything for one another and love each other with each fiber in our beings.
So, my brother. What a goof ball, ain't he? And by that, I mean, he is the most incredible guy I have ever come into contact with. It's interesting because he's all grown up now and is a man, but I will forever see him as the grubby 4-year-old. The boy who made mud pies in the backyard. The boy who wore cowboy boots and SpongeBob underwear and nothing else. The boy who I made dress up in pink dresses so I could have someone to play princess with (sorry for that). The boy who I grew up with. You will probably never have the opportunity to see him like that, but it is ingrained in my memory.
The only person on this entire Earth that knows exactly what it was like to grow up in my house, is him. I never have to try and explain my family to him, because he is the only other person who knows what I went through. We were enemies and best friends, at the same time. He's seen me at my best and Oh Lord, he's seen me at my worst. He has been my little brother through thick and thin, and I can't think of anyone else I would've rather grown up with.
But back to you, I am explaining how great he is (which I'm sure you know), but I just want to reiterate that you are a lucky woman. I'm speaking on his behalf and I am sure he is lucky to have you, also, but from what I know to be true, you are lucky. He has enhanced every life he has touched and will be a great husband and father. He is gentle, so kind, handsome, great with kids, just has a heart of gold, he has a great sense of humor, and is just an all around wildly amazing guy.
I want you to know, that I promise I will be there as your family continues to grow. I will be the best aunt I can possibly be and I know you both will do the same for my future children. Thank you for promising to love him for the rest of your life, because I did too the day he was born. Love you, and again, welcome to the family.
Your Future Sister-In-Law