Without knowing where you are it's tough to provide any real ideas, but if I am to assume the USA, then check around at your school, often highschools and colleges have LGBT groups which would be a place you could fit in. Far as your boyfriend, you know what kind of man he is, but remember he is young. I suspect if you mention to him that you are gender fluid but don't really plan to do anything, you just want him to know why you are acting strangely from time to time, he'd probably be okay with it, or I would hope he would. Your other option is to say nothing, make up some kind of cover story for those times and go to a therapist for "Depression" or some other cover and the therapist you choose just happens to also deal in gender matters and discuss it with them. Based on what you described it sounds like more of a gender fluid situation, but only a therapist will be able to say for sure. I wish I could give you a more concrete, do this, don't do this thing, but unfortunately I don't know your life nor am I living it, so the best I can do is give you options.

Thank you so much for your help, I'll look around for somewhere I can go to talk about this :)

I would first broach it gently and see how he takes it. Like make jokes about it or something lighter and see how he reacts? Also do you feel repressed feeling around him? I noticed esp in bedroom (if your doing that) it has been really challengin being with Cis boyfriends, unless they were okay with me, cause otherwise i get very repressed where they are always wanting to put me in a more feminine roll then I am comfortable with.
Or does he want to see in dresses as well? Things like that. Definitely if you ever get far like you will get married or anything I think you will have to tell him. Cause it will come up. But if you feel no need to tell him you don't have to either. But for me, dating cis guys have been hard.

I think for me cause of my transgenderness it has made me more attracted to very feminine men. Which often means gay. Which they never liked me cause I was not quite' man' enough.. And men that are straight, while i like them are hard, cause they want to make me more 'woman' then i feel. And even lesbians have had a hard time cause then they want someone who is more gender balanced I think. Anyways.. being attracted to males and being FtoM in my experience is a terrible disaster.
Though my first boyfriend was perfect cause even though he considered himself straight, he accepted and treated me like a male and he also cross dressed some, but just for me. Cause he liked me and wanted to make me happy. Anyway it was very nice.