Personally, I just can't imagine that vet school life is going to be harder than what life is like right now. More academically rigorous, yes. But seriously, right now most of us are working or taking classes full time, and doing the other part-time or both full-time, plus shadowing, plus volunteering, plus interning, plus clubs and community activities, plus stressing over educating ourselves on how to get ready for the application process, plus taking the GRE, plus whatever else we have going on, all on top of not knowing if we are going to eventually freaking GET IN or NOT.
Right now it seems like a year of vet school would come as a blessing, so that I only have to worry about doing ONE thing (even if it is one really hard thing!).
Not to be "that person", but that's what I thought too. I took 21-23 credits each semester, worked 15-20 hours weekly, was prez or an officer of multiple clubs, involved with a handful more, and was working on my thesis (and a new relationship during senior year). I was actually silly enough to think that vet school might even be less of a time-sucker than undergrad. For nearly all students, no matter how busy you are, I think you will find that you are very wrong.
The big difference to me is that you are in class from 8-4/5 just about every single day. You might have an hour for lunch but the rest is packed solid. There really aren't any more fluff courses (okay, we DO have a 1 credit behavior course this semester, but that still involves quizzes, a final, and a project) to fill out your schedule. After those long, very full days, most of us have to go home and study at least a little (< 1 hour) or a looooot (> 6 hours or an all-nighter) for most nights of the week. It's not that the material is waaaay harder than undergrad, but every class "counts" for something in your education (again, there's not much fluff) and there's so much material covered that simply keeping up with it, not necessarily understanding every detail, is critical.
Not only that, but commitment to other things outside of school is one of the awesome benefits (and dangers) of vet school. There are so many crazy, sweet things to see, do, and get involved with that you'll want to do them all! The hard thing is to take a step back and force yourself not to sign up for that wetlab or that meeting because a physiology exam is the next day. There was a falcon medicine wetlab last weekend that I badly wanted to attend...but I knew that I couldn't give up that much studying considering where I was in knowing the material. That being said, you will never be "bored" after school due to the number of clubs, activities, and educational enrichment opportunities available. Picking and choosing is the hardest part!
And of course, you meet some awesome people in vet school that you'll want to hang out with outside of class. Some nights, no matter what exams are the next day or next week, you'll get to have lots of fun with your classmates. I know that our class has routinely been dominating lots of trivia rounds at local bars, there have been several themed parties, and groups of us are always exercising together or going to movies or out to eat during down-time. You still WILL have time for these things! You just often can't be as spontaneous as in undergrad is all!
As far as relationships go, in our class we've had ones that have done really well this year and ones that have fallen apart. Vet school is not a blanket relationship death sentence - it depends on the state of a given relationship and the people involved. I've been with my guy for over two years and we've been long-distance since May 2009. NO problems for us! We're very fortunate because he has a job that has him travel every week, so he doesn't have much of an issue coming down here for a weekend instead of going home. He can even work from my place on a Friday and his company will pay for his travel. As soon as I get my syllabi in the beginning of the semester, I'll write all my exams and such into my planner and pick out weekends where the following week isn't loaded down with tons of work (since in those cases I'll need the previous weekend to study). Those "free" weekends often turn into our visiting weekends, and we've been able to see each other once every 2-3 weeks with us splitting the travelling duties.
It's a two-way street. You need to force yourself to make time for your significant other. They support and care for you, and as tough as it might be to put away your anatomy book one weekend, you need to carve out time for them. To me, making an A on exam and ignoring them is not as awesome as making a B and having a night to spend with your guy/girl. The best is when you can do both!
And they need to understand that you will be stressed, that your time to spend with them will likely be less, and that you still love and appreciate their support. Good communication, a solid foundation, and some specific date nights all go a long way. Like I said, relationships can get stronger (even the LDRs) and they can fall apart. It's all what you put into it. Mine is great - I have an amazing guy who fully supports this choice. Long distance is hardly a stress and we talk every night to bridge the gap. You can make it work!