When a thought of one of your boyfriend's ex-girlfriends comes into your head, immediately stop that thought from developing any further and bringing you down. It is essential that you do not let yourself dwell on the thought or, worse, let your imagination take control of your emotions by making up scenarios from the past. You will need to practice "thought-stopping" every day in order to be successful, according to WebMD. While it will take some work, the effort is worth the peace of mind that will result. The next time a thought about his ex tries to creep into your mind, say "Stop!" out loud, and picture your boyfriend with you instead. By replacing a draining thought with a happy one, you will gradually stop feeling insecure about your boyfriend's exes.

Talk to your boyfriend about how you feel so that he understands the thoughts you are struggling with. Most likely, he will assure you that you have nothing to be insecure about and that he is committed to your relationship. Just knowing he is aware of the challenge you face will help you feel closer to him and strengthen your relationship. Hiding your emotions by pretending to be invincible might be tempting, but it will not make everything all right, according to psychologist Dr. John Grohol, founder and CEO of Psych Central. However, be careful not to pester him with questions about his ex. Doing so will only further upset you and cause you to focus on irrelevant details of his past.

Focus on everything you love about your boyfriend and your relationship in order to stop letting your insecurities control you. Take the time to notice everything your boyfriend does for you and how much he loves you. Focusing on the past is a recipe for a life of unhappiness, according to William F. Doverspike from the Georgia Psychological Association. You may make a list of everything you are grateful for and then put it in a place you will see every day. If your life is full of positivity and gratitude, you will have no room to think about the past, much less dwell on it or allow it to lead to feelings of inadequacy.

Improve your sense of self-confidence by doing something for yourself, such as getting a makeover or beginning an activity that will take your mind off of your negative thoughts. For example, joining an exercise class will release endorphins, which will put you in a positive mood and make you feel good about your body. Improving your self-esteem will take care of the root problem behind your negative thoughts: the insecurity that is causing you to compare yourself to your boyfriend's exes.