All You Need Is Love

No matter what genre, the key for an emotionally engaging story is having the readers invested in your characters and their struggle. When a romantic main plot or subplot is in play, this means we have to not just love the leads, but love their relationship.
If the romance-- or unrequited romantic tension-- between characters is a key plot point, it needs to be believable and vividly rendered. The audience has to feel their love.
It's not just enough that the characters to declare their adoration for each other. This actually tends to be more annoying. It feels like the author is trying to bludgeon everyone into accepting the Twoo Luv in action, instead of showing us a pair we can cheer for. At best, all that your audience will be convinced of is that they're in lust. Show us why these two people 'get' each other-- maybe they share some common passionate interest, or compliment each other's personality and skills, or mesh over some mutual need. These are your characters, so you can develop their life stories and personalities so that the relationship makes sense and is a strong part of why the audience relates to the characters, not just a drama-generating plot crutch.