Back in the day (I have to put that disclaimer in there since I'm now in a relationship) I would never put a side chicks phone number under an initial, another girls name, or even work. Anyone of those will seem suspect when it pops up at 3:00 AM and lights up the entire bedroom. Instead put the name under your craziest male friend, preferably a single guy that your girlfriend hates. She won't even want to answer the phone if she hears it ringing and a crazy text will seem reasonable.
You get a text message late at night and she asks, “who the hell is texting you this late?” You reply, "It was Gabe." She makes a face of disgust and mumbles, “Uggghhh, why do you even hang out with that guy?” You reply, “I’ve known him forever. He's crazy, he just text me that he wants to blow me.” Then you show her the text as you laugh in her face. Your girlfriend will be annoyed and say, "Why does he text that? You guys are idiots. I can't stand him." You ask, "should I text him back?" She responds, "I don't care what you do, just don't show me his gay ass texts anymore."
Now you have the satisfaction showing your significant other a text of another girl saying she wants to blow you, disguised as your friend. She can see a text from him that pops up saying, "I'm pregnant" and she will still think it's that friend she hates. You feel like a genius and your girlfriend's feelings aren’t hurt. In addition, another girl is thinking about you inevitably boosting your low self-esteem and enabling you to hide your insecurities behind a selfish act of infidelity.