Sorry, but your dad actually has a point. Most folks these days don't end up having their 'serious' relationships (in terms of getting married, or entering into other kinds of long-term life commitments like buying property together or having kids) until their early 30s. And let me tell you, as a 33-year old, you still feel too young then. Now obviously, you'll have lots of relationships before then, but my point (and probably your dad's point)is that the current one isn't going to matter that much in the larger scheme of your life. She isn't going to be the women who, at 40, you'll be crying into your beer about, she isn't going to be the one who takes half your property in a divorce, and she isn't going to be the one you go cruising around the world with when you retire, or who looks after you in your old age.
Basically, relationships at that age just don't go past their immediate time-period. You will have many more relationships as you get older. Each one will have you thinking that THIS is the important one, where you've 'finally grown up', and which really matters. And then you'll get to the next one, and you'll think 'man, I didn't know anything last time - that was just me being a kid'. And that will continue for many years to come - hell, I still didn't really know what I was doing when I was in my 20s, during which I had a 6 year relationship and 3 year one. And I'm sure that in 30 years, I'll look back upon the earlier years of my marriage and think 'wow, we really didn't know what we were doing back in our 30s!'.
I know that jarrs. And the reason why it jarrs is that regardless of how insignificant this relationship is going to be in the overall scheme of your life, right now it feels like it's the most important thing you'll ever have. Oddly enough, the short-term emotional impact of relationships tends to diminish as we get older and they get more serious. You will never ever feel as massively unhappy as the very first time you get dumped. Even though this breakup will cost you nothing permanent, whereas future ones might take your house or your kids. And that's just because you tend to feel things more intensely, in the short-term, when you're younger. That's not a contradiction - in part, it's WHY our early relationships aren't so important. If you can get it where you are, find a book called 'High Fidelity' by Nick Hornby (don't bother with the film adaptation - it's a good film, but it leaves out all the stuff about his early relationships), it explains this stuff much better than I can (and it's a darn good book, especially if you're into music).
But when we're young, shorter periods of time seem much more significant than they do when we're older. A few months can seem like forever as a teenager, but by the time you're 30 that just flies by in the blink of an eye. Same with relationships - when you're a teenager, they seem to encompass your whole life, as if EVERYTHING will fall apart if you break up. As an adult, that same timespan and same degree of involvement is just trivial. That doesn't mean you don't care as much, or you won't be hurt - but it's a different kind of emotion, stretched longer: it's about having years of contentment, trust and happiness, or in some cases, the bitter slow bile of vindictiveness and a gradually emptying pit in your stomach. Your life 'falling apart' from a breakup, when you're older, doesn't mean a month of moping anymore - then it can be years of things slowly falling into ruin.
In that context, when your dad can look over and know full well that you're going to be fine in a couple of months, I can see why he'd make that comment. It's not about denying how strongly you feel - as I said, when your young the sheer intensity of emotion is at its peak. But as you get older, it's not just about the intensity of emotion, as that kind of all-enveloping passion (whether lust, love, hate or rage) dissolves as quickly as it formed.
