Ive done it before, but how do i do it again?

I am 5'6 and i weigh ruffly 155. I want to be smaller than that. Back in middle school I weighed almost 200 pounds and I was made fun of, I was called fat, lesbian, yada yada and when entered highnschool, I was still pushing 200. My whole 9th grade year I went through a transformation. I went from a size 16 to a size 10 in dresses. I lost about 30 pounds! It sounds great but I didnt do it in a healthy way. I stopped eating. All because i was bullied a little bit. I had joined a tennis team and when people asked how I did it, I lied and said it was because I joined a sport. But I felt happy that I lost it because people started to notice me. I started getting guys, I felt great, but now im a junior and ive stayed in the same weight range. 150's. It is good that ive stayed like this for a bit but now im tired of being this weight. I want to loose more, especially for the guy ive had a crush on since ive met him. I am having a fairy tale relationship right now cause im dating him. My best friend! He's in the Marines and hes coming home on his ten day next month. I cant wait to see him but hes always talking about how fit he has gotten since he joined....I have gotten jealous and hes the motivation that I need. I have the mind for it, I have the motivation, I just dont know how to start. I want to be his arm candy that he is to me. Its odd to say that but I want to look good for him. Where do I start, how do I lose some weight in a month?