i agree with both the above postings, but also you will feel better if you are losing weight for yourself, instead of your boyfriend, or some other reason, your boyfriend already likes you, or he wouldn't be going out with you....
When i was in 7th grade, i weighed 140 lbs, and i wanted to lose weight, so i limited myself to 1000 a day, and rode my stationary bike for at least an hour, if not more, each day. Once i got down to 120 lbs. i felt great, but it didn't last long, because i wasn't doing it for myself. Now i am 16, and 142 lbs, but i have recently started exercising, and watching what i eat again. It helps me to know that eating healthy and exercising makes me feel good, plus thinking of how i will feel, when i fit perfectly into that summer bikini helps :)