They know that they love each other, it's an unspoken rule. But every now and again he just wants to remind her of the fact that she's the only girl for him.

The first time he tells her he loves her she just found out that she was adopted
and that he was the one that saved her that faithful night on Wickery Bridge

The second time he tells her he loves her is the night of the school dance
after she so bravely fought back against an evil vampire that wanted to kill her because she looked like Katherine

The third time he tells her he loves her is when she's sitting in the grill
waiting to meet up with her birthmother.
She's so unbelievably nervous that he just needs to tell her multiple times
that whatever happens he'll forever love her

The fourth time he tells her that he loves her is the night he saves Damon from his fiery death.
He knows she cares about Damon and he also knows that she knows he's worried about that.
She tells him she loves him and only him
and later that night he tells her that she's the only girl for him and that he'll love her until his last breath

The fifth time he tells her that he loves her is the day he sees Katherine for the first time in forever.
He tries to lure her out to admit why she's here but in the process he just provokes her and she retaliates and stabs him.
Later when Elena's cleaning him up and inspecting his wound he tells her that she's the only girl for him and she has nothing to worry about.
He doesn't believe for a second that Katherine came back for him

The sixth time he tells her he loves her is right after they had their first vampire sex.
He knows she never wanted to be a vampire but she says that she found a couple of perks she loves about it and he just in return tells her that he is madly, deeply and irrevocably in love with her

The seventh time he tells her that he loves her is ironically the day they break up.
He knows he just can't do this anymore and that it's best for both of them to let go.
So, he does.
He tells her he loves her and walks away, utterly heartbroken and lonelier than he has ever been in his life.

The eight time he tells her that he loves her is the day they decide to give it one last try.
They have been rebuilding their relationship for the better part of a year
and they both feel that they're ready to give it one last shot. It's do or die, now or never.

The ninth time he tells her that he loves her is the day she becomes Mrs. Elena Salvatore.
They made it. He finally gets to call her his wife and they get to be together forever.

The tenth time he tells her he loves her is the day they attend Bonnie's funeral.
They both knew that witches didn't have eternal life and that someday they would have to say goodbye to her, they just never thought that it would hit them this hard.
They have seen many people around them die but Bonnie was just that one special friend you would want to hold with you forever.

The eleventh time he tells her he loves her is the night she comes down with a severe case of the flu.
They always thought that vampires couldn't get sick
but apparently when you're around children the odds are that you catch something are pretty high. Thankfully it doesn't last that long and she's up and running again the next day.

The twelfth time he tells her he loves her is after two centuries together happily married.
They celebrate intimately and privately and he tells her that he's still as happy with her
as he was the day he married her and that she'll forever be his one true love

The thirteenth time he tells her he loves her is the day they get to pick up their baby from the hospital.
They both know they would never be able to conceive babies the natural way so they decided to adopt. After a long and hard talk and lots of deliberation they decide to just go for it and the moment he sees her with this tiny little bundle of joy in her arms he knows they made the right decision. Elena is going to be such a great mother

The fourteenth time he tells her he loves her is the day they burry their baby girl.
They knew when they adopted that they would outlive their children and that was a choice they made. It doesn't make it any easier for the both of them though and when she tells him that she wishes they just turned her into a vampire around the age of eighteen he knows it's just the grieve talking and he just kisses her and tells her that they still have their son

The last time he tells her he loves her is the day they decide to end their lives together.
They have lived long enough, loved long enough, hurt long enough and grieved long enough to know that life has to end sometime.
For a vampire it doesn't have to but the day they got married was the day they promised each other that they would pick a day when they both would feel like they've lived long enough and they would die together.

So when that day comes and he tells her he loves her for the very last time right before they both lay down in the sun and take of their daylight rings he knows that he has been the luckiest guy on the entire planet and he knows he wouldn't change their journey for anything. They have had ups and downs, trials and tribulations but through it all they survived and came out stronger.
And he doesn't know of a better way to die than with his one true love next to him. And maybe there's a place for them in heaven, together.