i don't know what's changed

Before I came to uni I got with a guy who was a really good friend. We've been friends for ages and had been flirting for months. It was about two weeks before we left for uni. Coincidentally we're at the same uni doing the same course. Before we came we went on a few dates and it was lovely and I assumed it would just move forward at uni. But it's diminished to barely a friendship. We see each other and talk and have a laugh and then he goes off with his friends. I don't know how to bring up whats happened, especially as he's always with people and I feel a bit stupid. I've tried suggesting we talk cos things were weird but then I was ill and couldn't and then I texted him asking if he wanted to go for coffee after a lecture and he didn't reply. I'm really confused as before we came he seemed really into me and had said he had liked me the entire time he'd known me. I just don't know whats going on.