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A jealous girlfriend constantly fears that her boyfriend will leave her for someone else. This makes normal, friendly interactions you have with other women seem like grave dangers for the relationship. In extreme cases, this can even extend to your family members and mutual friends.  Example: You and your girlfriend are enjoying a pleasant lunch at the local cafe. When you finish, your waitress brings you the check. The bill is only $14, but you're feeling generous, so you give her a $20 and tell her to keep the change. She thanks you graciously and leaves. In the car, your girlfriend turns to you and spits, "What was that all about?" You ask her "what?", but she won't answer and stays silent for the whole ride. A jealous girlfriend won't trust you to behave when you're not under her supervision. When she can't chaperone you directly, she will often try to keep track of what you're doing from afar. She may get upset or angry if you can't (or won't) give her an exact record of your whereabouts.  Example: You and your friends are excited to enjoy a well-earned night out. Your plan is to meet up at your house before going to a movie. The night is a strictly "guys only" affair. While you're waiting for your friends to show up, you get several inquiring texts from your girlfriend asking about your plans. You field these for a while, but eventually turn off your phone for the movie. As you're leaving the theater, you switch it back on to find a string of frantic texts and missed calls asking about what you're up to. Your girlfriend is furious the rest of the night and gives you the cold shoulder the next time you see her. Jealous girlfriends may suffer from irrational fears that their boyfriend is being tempted by the other women in his life. Their desire to uncover the "truth" can lead them to ask or suggest things that aren't usually appropriate for casual conversation. These can have to do with the other woman's relationship status, her sex life, the nature of her relationship with the boyfriend, and so on.  Example: You have a (strictly platonic) female friend that you've been close to since kindergarten. However, you haven't seen her for a year because she has been in a study abroad program. The day after she gets back, you meet for lunch to discuss her adventures. Later that day, when you meet with your girlfriend, she asks you questions that make you a little uncomfortable: "So did she get with any foreign men? Did she come on to you? What was she dressed like?" Jealousy can make romantic partners stop respecting each others' privacy. Trust, which is the foundation of a strong relationship, gets set aside in favor of petty suspicions. If you uncover evidence that your girlfriend has been going through your possessions or your correspondences with other people, jealousy may be the cause.  Example: When she's at your house, your girlfriend asks to use your computer for a few minutes. You don't think anything of it until a few days later, when a friend asks you, "Why didn't you reply to my message?" You log into your social media profile to discover that several new messages are marked as "read." When you ask your girlfriend, she gets defensive and refuses to talk about it. It's very difficult to be consumed with jealousy and not show any sort of external sign. Most people who are jealous of their significant other will gain a certain hard-to-define tenseness around them. Conversations may seem "forced" and happy emotions may seem somehow fake. Fights and petty arguments may become more common.  Example: Ever since you went to your best friend's bachelor party, your girlfriend has been acting a little strange. You can't quite put your finger on it, but it seems like she's got something worrying on her mind that she won't acknowledge, even when you're having a good time together. When you ask her about it, it seems like you always end up getting into a fight about something unrelated. The way you feel can also tell you about the state of your relationship. Do you feel slightly anxious when you're around your girlfriend? Does part of you dread your meetings with her? Do your favorite activities and date ideas not seem to lead to the same sorts of happy emotions that they used to? There are many things that can lead you to answer "yes" to one of these questions, but if you've noticed some of the things above as well, jealousy may be the root cause.  Example: You can't lie to yourself. You're a little worried about the road trip you're set to take with your girlfriend over the weekend. It's not that you're not excited to see Mount Rushmore — in truth, it's that your girlfriend's behavior has left you feeling on-edge lately. The idea of having yet another argument makes you feel emotionally drained and it hasn't even happened yet.

Summary:
Look for anger or defensiveness when you talk to other women. Listen for lots of prying questions about your activities. Listen for inappropriate questions about women you know. Look for signs of inappropriate snooping. Look for a tenseness or anxiety in her behavior. Search your own feelings for fear or anxiety.