Those perfect three words

So full back story, I met my boyfriend when we were in high school, our senior year. I was always super attracted to him but we were in very different places in our lives and it never went anywhere. Over the past three years we had gotten back in touch every now and then and we always flirted but it's stop after a few days. This past May was my birthday, and he wished me happy birthday and we started talking again. I turned the big 21 so he went out with me and some friends and a few days later we were exclusive. We'd only been dating for about two months, and part of me wasn't actually sure how he felt so I didn't change my typical flirty ways and he went through my phone and thought I was cheating on him. I wasn't at all, he's the only person I think about in any romantic way, but the thing that sucked the most is he said he was thinking about saying he loves me. And I guess I wasn't sure truly how he felt until that moment. It's been a few weeks since that happened and I want to tell him I love him, because trust me I do, but I'm afraid he isn't ready for that or he won't say it back. Advice? Sorry for the long post