Summarize the following:
Let your boyfriend know you want to have a conversation about your relationship. Telling him ahead of time lets him get prepared for the conversation, so you're not blindsiding him out of the blue. It also gives you a chance to pick a good time to talk.  If you pick a time, it can keep you from blowing up in anger in the moment he flirts because you've had a chance to talk about it. When you do talk, make sure you have some time to do it, and you turn off the electronics so you don't get distracted. Start the conversation from what you're observing and how it makes you feel. That way, you start out by helping your boyfriend see where you're coming from. You don't want to blame him, as that will just put him on the defensive. Focus on what you're feeling. You could start by saying, "I notice girls flirt with you a lot. I like that you're attractive. It's one of the things that made me want to date you in the first place. However, it upsets me when you engage in the flirting instead of trying to shut it down." You may know why flirting is a trigger for you. For instance, maybe you've had flirtatious boyfriends in the past who ended up leaving you or another girl, and therefore, when your boyfriend flirts, you're afraid he's going to leave you for another girl.  You may need to spend some time thinking about the problem to figure out why the flirting bothers you so much. Often, it comes down to trust. You could tell him, "Flirting bothers me because my old boyfriend, Jake, used to flirt all the time, and you know he left me for another girl." Now that you've started the conversation and explained how you're feeling, you should give your boyfriend a chance to have his say, too. For instance, he may not even realize he's flirting or maybe he didn't realize how much it upset you. Maybe to him, it's just being nice to other people.  Pay attention to what he's saying, instead of trying to think of the next point you're going to bring up. Don't just focus on your hurt. Listen to his feelings and intentions. Nod and ask leading questions to get to the heart of what he's saying. For example, you could say, "I feel like what you're saying is that you don't see flirting as a big deal. Why do you feel that way?" Flirting is often connected to jealousy. Maybe he's intentionally flirting because he wants to make you jealous. Maybe you're overreacting because you have a tendency to be overly jealous and protective. Open the conversation to see if jealousy is a part of the problem.  For instance, you could say, "I know I've been acting overly jealous. I think I have a problem with you flirting because I feel like I'm not enough for you." You could also ask, "Do you sometimes flirt so that I will feel jealous? I only ask so I can figure out how we can fix what's wrong with our relationship that would make you want to do that." Let him talk about how he thinks jealousy is affecting his flirting to help continue the conversation. Once you've both discussed your feelings, talk about how you can make it better. You may need to compromise to figure out a solution that works for both of you, so that both of you have your needs met as much as possible.  One way you could compromise is to reevaluate what you consider flirting. For instance, maybe you could start to see him having a friendly conversation with a girl as not flirting, even if you considered it flirting before, while if he's touching her or leaning towards her, you could consider that flirting. Find ways to let him know when you think he's going to far. For instance, you could whisper in his ear when you think he's flirting too much to help get his attention. Talk about it as it comes up. You don't need to have a serious conversation in a restaurant. However, when you feel like he flirted too much, try to talk about it within a day, so he can realize you're feeling hurt and help to rectify that. Be more intimate. Sometimes flirting can come from a lack of flirting with you. Take time to hold his hand, kiss him, or dance with him on the porch. All the little things add up to make you both feel more loved and secure. One final option is leaving him. If you can't stand the flirting and it bothers you enough to make you upset on a regular basis, you do have the option of getting out of the relationship. Sometimes the only option is putting up with it or getting out.
Prepare your boyfriend ahead of time. Talk about your emotions. Explain your emotions. Let him have his say. Discuss jealousy. Find solutions. Leave him.