^^^ Pretty much got to agree with 'ilikestims' there...
But yea, I wanted to speak on this for a second -
My second relationship, and my first really, really serious one, took place when I was 17-18, and it was 'long' distance, although we were just living an hour apart. We had sex a few times, and then she went off to college (she was actually younger than me but a year ahead in school), broke up with me right before she went, reconsidered, really wanted me to come to her college a days' drive away and visit her (although I really did not have the time at all to do this - was busy with extracurricular activities all the time) to have sex, and then a month or so passed and she told me that she had slept with a ton of dudes and yea, I really wasn't interested in her after that.
I'm not putting in all the details about how we got together and how close we were because that's beside the point here - our relationship was near doomed from the start because we really weren't able to put in the 'relationship' time. Now, your case does sound somewhat different, but, honestly man, if you were the one who cheated on her and she came back to you she's either hopelessly naive/'truly in love' with you or she just thinks that you guys are like truly meant for each other in the end, regardless of some flaws that might pop up along the way...
You understand you're talking about being committed to someone else for the rest of your life and you guys don't even interact in close quarters more than 12 or so times a year (I know I'm simplifying what you said, I'm just saying) AND you openly admit to readily cheating on her and basically getting back together with your girl, like, for her? Not to be disrespectful, because you DO seem like a perfectly cool dude, but that's a little fucked up, man.
I've seen plenty of friends' long distance relationships crumble to the dust after a year or two, three max, in college, and trust me, all those couples absolutely LOVED each other - but people can really change in college, especially by senior and post-grad years. My own long distance relationship, which, albeit, was always long distance, only lasted for a few months even though it was really intense and I don't regret it.
I might be biased, admittedly, but I'd tread with a ton of caution. It's up to you what to do, but just think it over very carefully - you're talking about very deep shit committing to someone in this day and age, what with all the fluctuations in personal life and economy that's going on RIGHT NOW. Anything could happen between you guys, honestly, just be prepared, lol, like the Boy Scouts.