I really like her, but there's uni

Anon please, as people know me personally on here. I recently went out with a girl, who was my first everything bar kiss. It wasn't a particularly long relationship, only 3 weeks, and this is mainly due to the fact that I'm afraid that if I have a (long distance) girlfriend when I go to uni, then I'll miss out on the whole experience, especially freshers. Also, as we'd only been together for a few weeks, I didn't think it'd be "strong" enough to last whilst we were apart. However, as it was such a short relationship, we've decided to stay friends, and whilst I thought I'd be fine with this (especially as I was the one who broke up with her), I'm really not. She keeps dropping hints that she wants to get back with me, but as we're going to different uni's, and we're already a good 30 minute drive from each other whilst back at home, I feel like it wouldn't work. She's already at her freshers, and I know that she's slept with someone there. When I found out (she told me), I kept a straight face but inside I felt my heart sink, like a dull ache. I think that I've majorly screwed up; I've broken up with a girl that I really like for the chance of perhaps of a bit of casual sex whilst at uni, something that I'd most likely not be able to instigate anyway as I'm quite shy. I genuinely don't know what to do - do I ask her out again (she's coming back for a few days, I'm seeing her, we've sort of got a FWB thing going), or do I keep it as it is? I'm also worried that if I start going out with her again, I'll reconsider it again, which wouldn't be fair on her at all, and would probably ruin any chance of remaining friends that there is, which I wouldn't want! I realise this is a bit rambling, but any advice would be seriously great. TLDR; Like a girl, went out, broke up because of uni, think I've made a mistake, have I?

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