ABSTRACT: While teenagers will form relationships at school and these are part and parcel of growing up, it is dangerous and over simplistic to actually describe them as 'true love', much less extrapolate them to marriage.
It is part and parcel of growing up for teenagers to form boy/girlfriend relationships and JK Rowling does capture this aspect of her characters very well. It is fun to try and read between the lines and try and tease out unseen relationships between characters - Neville and Luna being an obvious one. However it becomes a dangerous pursuit to try and extend such speculation to infer the sort of 'true love' and bond that leads to marriage.
I say dangerous for two reasons. First of all the motivators that lead two people to marry are complex and adult in nature. They are not explored or even touched on in any of the novels, nor do they need to be. To do so would eclipse the central plot and narrow the audience. Second, to be able to speculate on such matters with any authority means that you need the experience of maturity to see things in perspective and context. This is not said to denigrate any of Mugglenet's contributors, but merely a statement of fact.
Let's talk reality for a moment. Relationships formed at school in your teenage years rarely lead to marriage. Yes, at the time they can be very intense, may seem like 'true love', perhaps are true love within bounds of teenage experience but by its very nature, teenage experience is very limited. These feelings are totally new and nothing like the sort of love felt for say a parent or sibling. It is completely natural for such feelings to have (for the moment) an unbelievable intensity only to ebb away equally quickly. Then there are the natural teenage insecurities surrounding the fact that if you don't have a boy/girlfriend and are therefore not 'in love' there's something wrong with you... and again JK gets this right on a number of occasions. Remember Ron in Half-Blood Prince with Lavender? At first he's all over her and then he can't wait to end it with her...
Not surprisingly, when you leave school and go on to university or college or start work, your perspectives change radically. You meet new people outside the closed world of school, are presented with new opportunities and challenges in life. In short, you grow up. What was important at school becomes less important. Relationships which were oh so intense at school become rather less so especially when you mature at a different rate and in different directions to your partner - hear the phrase 'grow apart'? Under such circumstances, the idea of tying yourself down to one person you've known since childhood becomes less and less appealing, at least until you've experienced life long enough to really know that that person is indeed right for you.
And then there's the matter of physical attraction.... the dreaded 'S' word. Although it, quite rightly, has no place in Harry Potter, it is an integral part of attraction between males and females of whatever age, even as a teenager and especially as you grow into maturity. In reality you can't leave it out even if it's not mentioned in the novels.
Not that I'm saying that childhood 'sweethearts' (what a dreadful phrase) never go on to have a happy marriage. Only that it happens very rarely.
So how does this relate to Harry Potter? Quite simply this. The relationships... and potential relationships... described in the books are those of an almost idealised innocence. The description of the characters' feelings are well managed but there is only a fleeting hint at a deeper passion and that's only with Harry and Ginny in Half-Blood Prince. Yes there is a depth of feeling but how much of it is genuine and how much of it is simple teenage angst?
If these relationships are at best childhood crushes they are no indicator whatsoever of anything that would last beyond the 7th year and out into the big wide world. Any putative connection between Neville and Luna for a lasting relationship or even marriage is therefore meaningless, as is the reasoning for any other coupling.
So, you might ask, how come right at the end of Deathly Hallows we are presented with Harry and Ginny and Ron and Hermione as married with children? How indeed? Apart from their life long friendship (at least between Harry, Ron and Hermione) what else is there to drive this? And here, I think JK Rowling really does have to fill in the blanks, at least up to the point that the two couples marry five or six years out of Hogwarts. Harry and Ginny you might just imagine, but Ron and Hermione?
It is said that the sharing of a momentous, life changing experience (such as the battle of Hogwarts) can bring people together, but equally, once that reason for being together is removed and normal life resumes, the relationship disintegrates as there is no shared focus. So... there has to be something else... something adult, something that is outside the bounds of what would be appropriate in children's fiction.
If JK Rowling were ever to write the post Hogwarts story and how these couples eventually marry, she'd have to cast this as a very adult story for it to be believable. The trouble then would be that, in doing so, she would almost certainly alienate her younger fan base and I wonder, much as I admire her, if that's the sort of writer she can be or wants to be.
The conclusion has to be then, that there is absolutely no way you can predict which HP character will form a relationship with another beyond the idealised innocence of the world JK Rowling describes. Actually that's not quite true. You can do this, but you would need to ascribe characteristics that are outside the realms of children's fiction and have the experience of mature years to understand and describe their implications.
And... yes I am of 'mature years', I am married (and to someone I met years after I left school) and all of the feelings I've described above are absolutely true. I've been there and, as they say, got the T-shirt.