The thing I love about Logan and Veronica is that, they both lost their first loves (Lily, Duncan), so in most cases it would seem like they were just 'settling' for each other. But for them, it was the opposite.

They both lost their first loves in extremely traumatic ways. Logan's first love Lily was murdered by his father, and Duncan ran away to Mexico with the child of his dead ex-girlfriend. In addition, Logan had been left down by pretty much everyone in his life, his father murdered his girlfriend, his mom committed suicide, none of the 09ers really understood him, and everyone just saw him as the son of Aaron Echolls. He didn't really feel he could trust or rely on anyone other than Dick, but Dick is well, Dick, so that's not saying much. And after all the turmoil with her rape, Lily's death, and her mom, Veronica only had her Dad and Wallace, and she was closed off and didn't trust anyone or open up and make herself vulnerable to anyone.

However even when they absolutely hated each other, they had an unspoken connection that had formed over the death of Lily, even though that was ironically the event that created the hatred between them anyway. When Logan asked Veronica to help him with his mom, it wasn't only because Veronica was a P.I., it was also because he knew he could rely on Veronica and that she wouldn't judge him, and he trusted her enough that he broke down in her arms when he found out his mom was in fact dead. In 1.18, Logan comes to save Veronica at the Camelot which leads to the famous first kiss, even though they are still supposedly enemies at this point. Even at the end of season 2 which could quite possibly be when the levels of tension between Logan and Veronica were at their highest, Veronica still texted Logan to come and help her when she is on the roof with Cassidy, because they know that no matter how much hostility is between them they will always be able to rely on each other.

I think Logan has always had a bit of a crush on Veronica, which he shyly admits when he said he thought she looked 'hot' in her soccer uniform. They are really alike in the way that they both have like explosively strong personalities, and a sarcastic attitudes, but underneath all that they are really broken up. But those strong personalities mean that all the emotions they have for each other are strongly amplified. That's why they struggle with their feelings for each other at first. They have such extreme loathing for each other but then when Veronica kisses him in 1.18, it was intended to be a small thank you kiss, but the feelings they have for each other take over and it turns into a passionate kiss. Then they both have conflicting emotions, because what are you supposed to do when you start to have such passionate feelings about someone you hated so much?

But then, in the next episode Logan and Veronica decide to give into their feelings and they say:

Veronica: I know Lilly loved you.
Logan: Just not like I loved her. It's ok. You know it kind of lets me off the hook. You know, I don't have to feel guilty anymore.
Veronica: Feel guilty about what?
Logan: Moving on.

I think this is one of those moments that really defines their relationship. This proves that even though Lily was his first love, she wasn't necessarily his strongest. It took SO much strength, to get over all the pain and turmoil that they had been through since Lily's death and loosing the ones they loved, and having to deal with all the emotions that have a relationship brought along. But the love and passion between the two of them was able to overcome all that grief and pain to allow themselves to give their hearts to each other. Neither Logan nor Veronica had such a strong connection with another person and this has been proven countless times. To name a few:

1. When the 09ers find out that Logan is dating Veronica, instead of laughing it off, or running away he tells them that if they don't like Veronica they have a problem with Veronica they can leave or just 'evaporate'. And then leaves the party to be alone with Veronica, not just to make out but to be honest with her and tell her about his (unintentional) involvement in her rape. This shows how much Veronica means to him; he is willing to stand up to all his 09er friends and will ditch them to be with Veronica. This shows that Veronica has become the most important person in his life and he is willing to do anything to make her happy.

2. Logan's reaction to their breakup and erratic behavior in season 2 shows that after he lost Veronica he was put on a downward spiral. Like he said he's 'tortured, ever since he I got his heart broken'. Although he was sleeping with Kendall Casablancas and dated Hannah for a bit, it was obvious that his feelings for Veronica were always there which were verified in the famous Epic speech he gave to her at the alterna-prom.

3. One of my favorite Logan and Veronica episodes is the Season 3 episode "Show Me the Money" because it proves that Logan and Veronica literally can't function without each other. This episode is six weeks after the previous episode when Logan and Veronica broke up, and both Logan and Veronica are very melancholy, and not really themselves, throughout the whole episode - especially Logan who can't even be cheered up by his favorite things, according to Dick (surfing, booze, girls). But none of those things matter because he doesn't have his favorite thing of all - Veronica. Finally after having a talk with Piz about not letting things pass her by, Veronica goes to Logan's hotel room and they reunite without having to say a word, because they both know they can't live without each other.

Together they have experience and supported each other so much, and Veronica and Logan will never have the history, connection, chemistry, or bond of love, passion, and understanding that they share with anyone else.