have I outgrown him?

I got together with my boyfriend when I was 15 (he's 2 years older) I'm turning 18 in a few months, and I just feel that I've grown up and changed a lot when we were together, and kind of don't know who I am without him? Sometimes I feel like I'm only with him because its normal and familiar, I do love him but our relationship is strained at times because he attends uni in another country. He says he grew up and matured a lot before he met me and is really serious about our relationship and has even mentioned marriage, this scares me: he was my first boyfriend and I just think how can I know what I want if I've never experienced it? I don't want to talk to him about it incase it hurts him or we break up and I realise our relationship is what I wanted. Any advice? :(

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