Many children can be very protective of their moms especially when it comes to dating. 
However, one mother decided to address the issue by writing an open letter from a teenagers perspective to any future men that are interested in dating their moms:
Dear Dude,
I get it. My mom is pretty awesome. I understand why you'd like to spend time with her. You and I may not have met, but I thought you should know a few things before you date my mom.
1. She's my mom. You have one. You know what I mean. She's that woman who brought me home and fed me and changed me and took care of me when I was sick. Sometimes she still does those things. She doesn't tolerate backtalk and lying from me anymore than your mom tolerated it from you. You will respect her the way you respect your own mother.
2. I'm her kid. She may care for you. She may even love you. But no one will ever matter to her heart the way that I do. You might be in her life for a day or a few months or even the next thirty years. I was here before you, and I will be here no matter what.
3. I don't need another dad. I have one. Even if he's not here when I would like it, I have a father. If you stick around for a while, and you and I get to know each other, don't expect ever to take his place. You can't. I won't let you, and neither will Mom. If you want a relationship with me, you'll have to find your own way to connect with me.
4. My mom is the most beautiful woman in the world. She complains sometimes that her thighs are too big. She swears those new gray hairs and wrinkles are a gift from me. But even when she comes in to wake me in the morning and her hair is crazy and she doesn't have on any make-up, she is still the prettiest girl I've ever seen. Don't ever make her feel like she's not.
5. My mom isn't perfect. She gets mad sometimes. She yells. Sometimes she gets really quiet and just smiles at me, especially if I walk in on her crying. She won't admit it, but I think she's scared sometimes. She went through a lot with my dad, and so did I. She's having to do a lot by herself. But even when she screws it up and forgets to sign my permission slip or get milk at the store, I know she's doing the best she can.
6. My mom is busy. She's working and taking care of me while running our house and trying to spend time with you, too. There's a lot for her to do. She doesn't just sit around on the couch, waiting for you to call her. If she's important to you, respect her time. Understand that she can't drop everything, especially me, just because you're trying to get her attention.
7. My mom is special. There is no one else like her. Yeah, she can make me mad, and I do stupid crap to get her attention or get back at her for not letting me go to that party last weekend. (It doesn't matter that I'm failing math. Jack's mom let him go, and his grade is worse than mine!) But she cooks my favorite food and kisses me goodnight and tells me every single day that she loves me. No one else would do that for me. If she does any of that for you, you'd better remember how lucky you are. I know I am.
8. My mom deserves to be happy. She has been through a lot. We all have. Divorce sucks, and it hasn't been easy. It's getting better, though, and no one has the right to screw that up for her. I know grown-ups have bad days. Sometimes they argue. But you don't have the right to make her sad. Ever. If you do, you'd better apologize and try your hardest never to make that same mistake again. That's what she taught me. Hopefully your mom taught you the same thing.
9. I am watching you. I'm still trying to figure out my place in the world, and I pay attention to everything. It'll make me mad if you treat my mom badly, but it'll also set a bad example of how men should behave. If you're a jerk, I'll think it's okay for a woman to tolerate that.
My mom is a grown woman. She can make her own choices. For whatever grown-up reasons that may or may not have anything to do with me, she has decided that you are worth her time. Acknowledge that. Respect that. Treat it right.
And remember that my mom is awesome. She's got me -- how could she not be?
Mama's Little Baby