Been in mine for 3 and a half-ish years. It's been amazing. Not sure where it's going from here, though. For a year-ish recently we were doing it long distance and while it was fine and we didn't run into any problems, we both decided we'd not want to do it again. In September we'll both be going quite different ways and distance will become a real issue for the long term, so... we don't know if realistically we want to carry it on. I think we're up for trying but knowing how we felt after the last time we went long-distance, we can't really see it working out. So, as much as we both love this relationship, it's a little bit uneasy at the moment.
It's a shame really since yeah, it was getting quite "serious" (or at least, as serious as it can be at this sorta stage), and in the future we'd both have wanted to take it a bit further we think. Maybe that'll still happen, but it's really hard to say at the moment.
Re: tips for people not in relationships, none. "Dating advice" is a dumb concept. There are literally billions of people out there who you could end up with, and there's no one formula that fits all - or indeed, many - of them. Just try whatever and if it doesn't work then you and the other person didn't match at the time.