Neither one of you is ready for a relationship. Friendships, absolutely, but not a committed relationship. You’ve been working against nature. The teen years are supposed to be a time when you try on a number of relationships in order to figure out what kind of person you want to be and what kind of person you want to be with. Instead of letting yourselves have the freedom to make lots of friends and to gain experience with the other sex, you two have been trying to act like you’re married or something. You call your boyfriend’s interest in other girls “cheating”. I call it normal looking around. You say your problem is your jealousy. I think the problem is that you don’t really believe that someone wonderful will stick by you. You blame your lack of self-confidence on your boob size. Frankly I doubt that a boob job is going to help. You’ll just be the same insecure person with bigger boobs.
Even though it’s painful, what you and your boyfriend are going through is perfectly normal. You both have good instincts. You know that you aren’t ready to be committed but you keep fighting with your own good sense. You both know that you have personal work to do before you can make a commitment. You need to work on loving yourself, regardless of the size of your boobs, your nose, or your earlobe. External stuff like that isn’t who you are. He needs to have enough experience with women that he can settle with someone without wondering what he is missing.
I suggest give yourselves and each other room to learn more about the other sex. Go out with a variety of people. Have fun. You don’t need to settle into a committed relationship yet. You do need to commit time to making yourselves into someone who can.
I wish you well.