I think it's being portrayed as a very compelling love story, which it undoubtedly is, which isn't the same thing as a wonderful love story.
I don't see it as a love story in the conventional sense at all. They're both on their way elsewhere, they are each the ones who launch the other towards their real lives.
By the end of the novel, Marianne has become a 'normal person'. No one stares at her on campus any more, she's not gossiped about. She's cut herself off from her abusive family (and it's never stated, but the fact that she now has a PT job, lives in scholarship accommodation in TCD and eats in the dining hall suggests she no longer accepts their money either). Her scholarship will cover a postgraduate course. She's free.
Connell is on his way to becoming a writer, editing the TCD literary magazine, and has been accepted onto an MFA in NY -- but this is all because of his literary friend Sadie, who encouraged it, just as Marianne encouraged him to apply for English at TCD. He hasn't even told Marianne he applied, and she doesn't want to go to NY with him, anyway.
The last scene of the novel has them acknowledging their love for one another as a given, but also, from Marianne's POV:
'All these years they've been like two little plants sharing the same pot of soil, growing around one another,contorting to make room, taking certain unlikely positions. But in the end she has done something for him, she's made a new life possible, and she can always feel good about that.'
And she also thinks that, whether Connell returns from NY or not, they will never get back again what they have now, but that he's done more for her than she has for him, he's cured her of feeling 'unworthy'.
The very end is Marianne setting C free to go to NY (when he's still asking her to tell him not to go and he won't -- she's being the adult here):
'They've done a lot of good for one another. Really,she thinks, really, People really can change one another.
You should go, she says. I'll always be here. You know that.