My first love is fizzling in and out... what do I do?

Okay, so my boyfriend and I are seniors in high school and have been dating for nearly eight months. At first we were totally in love, then the "first phase" wore off and we started having issues since I wasn't sure I loved him, he was too clingy, I wasn't attentive enough... it was a mess. Lately we had been doing a lot better, he is working on his clingyness and the way he gets mad and judges me a lot, and I'm working on being attentive enough... even so, my feelngs keep flip-flopping. One week I'll love being around him and being with him, the next when I'm with him I'll feel nothing more than... friendship? Then we'll have a fight and I'll feel close again. I don't want to break up with him... he's my first love, I want so badly to go with him to prom and everything and enjoy the summer with him... how do I get the flip-flopping to stop and just stay loving? Another issue is that I'm scared for the future... I'm not ready to settle down yet, and I feel as if we are married.