Am I horrible to be thinking this?

I'm posting this anonymously because I honestly feel awful for having these thoughts but I desperately need someone's opinion... Me and my boyfriend are 18, we've been together officially for 3 years although I lost my virginty to him when we were 13 and we had a kind of relationship for a bit but we were obviously very young and went our different ways, were with other people ect. I know 18 is still very young but my point is we have a lot of history and we both consider this a serious relationship. 
We're going to university together in September and always talk about how excited we are to start our life together and be able to have our own place, independence and eventually a family and all that grown up stuff 😳 99% of me knows I love him and even though I realise we might break up as we're both young and have our whole lives to meet other people, I really don't want that and only want him. Buuuuuuut there is this 1% that thinks maybe he is not the person I'm meant to be with?? I don't have feelings for anybody else and the thought of us breaking up/me being with another person makes me nervous and so sad... It just makes me feel weird. But at the same time the thought of meeting someone completely new and exciting at university has been crossing my mind more and more lately :( is this horrible or just normal? Please don't judge me I really do feel terrible about it 
:(