Definitely agree with purplelamp. Calmly explain to him how you love him but don't quite feel ready for engagement yet - that's not a remark on your relationship as much as it is your age. The fact is, if you were going to break up at university then it would happen no matter if you're engaged. It's all about making the effort to maintain communication on both ends, that is what will keep the relationship strong, not an engagement ring.