Love is very hard to understand. It can vary as much as there are people since we all show love differently. Some spoil their loved one, some just can't bring themselves to say it, some deny it or doubt themselves, some are very open about while others are secretive. Love can be fluffy, hot, uncomfortable, and even hurtful. Depending on who your characters are, how they'll express love becomes different and they'll react to it differently.
If I remember you're the one who had a married couple right? And in another thread you asked about kissing right? Anyways, my main point it that there is no definite theory on love. It changes with your character.
For example: Let's say it's a gloomy girl who has a male friend who was always nice to her. They went to the same school for years and he was nice to everybody except she was the only one he really talked with. Be it about anime, manga, or just life in general he would always find a way to start a conversation with her. Her, being a little paranoid, took all of that as just him being kind because she was in love with him. Since she was in love with him she wouldn't even think that he could be in love with her. Sometimes loving someone too much closes the door for love.
Not sure this made any sense... (. _ .ll)
I'll try to put it another way. Love depends on the person.
If you're wondering how people know its love: They become very conscious about the other person, they stare a lot, a tight fluttery feeling happens when said person is near, you find yourself wanting to be near them, want to know what they're doing, getting suspicious about who they're talking to and being protective in general. Laughter come more easily near said person, they ease your heart by just being near them, in your eyes they'll always look beautiful (or handsome), you want to be closer than just friends, you accept their flaws no matter what they are and they do the same for you. Physical touch like hugs or kisses become a need, spending any kind of time together brings you bliss.
.... Oof, yeah.... Again, not sure if this makes any sense...
Hopes this helps! (even just a little bit, not the best at explaining)