Love really hurt don't you agree? it is what that make alpha male become a beta male. hahaha. This is even true if you see your gf as your future wife which you will end up spending the rest of your life with and you feel like you don't wanna lost her. If you view it that way, your bargaining power start to decrease while her increase. You are a man dude who's bargaining power increase when you reach 30 while girls decrease when they reach 30. Why is that? Girl attractiveness decrease a lot as they aged while guys just decrease very little. Plus she is 18, meaning she is in the top in her game and even top if you show DLV on her by showing you are concern about that guy texting her. It show that you are threaten by that guy and also show since you are threaten, that can mean (for her) that guy is better than you and so if that guys is better than you, then..... think about it. Girls love to be attracted to a more better guy. Just like what the previous reply post say, have more girls attracted to you in your social circle. Have a sense that you are the guy with plenty of option that if you lost her, then, you still have a plenty more to go.

Anyway, as for your remedy for this (since she might see you now as someone lower than her and girl are not really attracted to that), surround yourself with a girl who is at least better than her and also surround yourself with someone who is perceive as higher value so that your value increase. And also i suggest that when you with her, introduce her to one of you female friends, and qualify that female friends of yours in-front of her subtly (so that it subtly show ur gf there that there is one other girls who is better than her and a quality present in other girls that you find it worthy for your attention and attraction). You need to increase your value (DHV) now man! Have a mindset of mind abundance, not mind deficit. You are the alpha man dude. You always have choice. Time is on your side! There is plenty of girls out there. Girls who is in her top are not really serious about a relationship with someone who she perceive low. The bargaining power is in your hand. But of course, you also need to give her what she need, as a man! And what quality does a man have? Just search it in the internet. ha ha ha