The full list, as far as I know, from the file LTR_Romance_Main. Some of those are strange. And yes, there are two stages named "lovebirds".
Friendship -100 to -70:
- Romance -100 to -50: Total Opposites. "One says "hot" and the other says "be quiet". One says "black" and the other says "go away". What total opposites!"
- Romance -50 to -10: Terrible Match. "It's probably best to stay apart. There's a lot of dislike here. Like, a lot."
- Romance -10 to 10: Despised. "Things in this relationship have gone awry. Can it be salvaged?"
- Romance 10 to 50: Hot and Cold. "Are they on or off? People can never tell."
- Romance 50 to 100: Enemies With Benefits. ""I hate you...but I must have you!""
Friendship -70 to -20:
- Romance -100 to -50: Terrible Match. "It's probably best to stay apart. There's a lot of dislike here. Like, a lot."
- Romance -50 to -10: Bad Match. "Sometimes there's just no chemistry."
- Romance -10 to 10: Disliked. "This relationship is tense. Things are likely to go awry!"
- Romance 10 to 50: Hot and Cold. "Are they on or off? People can never tell."
- Romance 50 to 100: Hot and Cold. "Are they on or off? People can never tell."
(Yep, it repeats the same relationship here. Same file even.)
Friendship -20 to 35:
- Romance -100 to -50: It's Very Awkward. "They drive each other crazy, but they also drive each other "crazy...""
- Romance -50 to -10: It's Awkward. "At least some aspects of the relationship are budding, if not all."
- Romance -10 to 10: Acquaintances. "Neither friend nor foe - just an average relationship"
- Romance 10 to 25: Romantic Interest. "It's too early to tell, but there could definitely be something there!"
- Romance 25 to 50: Lovebirds. "A connection of curious hearts. This is shaping up to be a beautiful romance."
- Romance 50 to 100: Lovers. "To be in love is a beautiful thing!"
Friendship 35 to 60:
- Romance -100 to -50: Bad Romance. "Sometimes your gut tells you it's all wrong. And then you tell that gut to be quiet."
- Romance -50 to -10: Awkward Friends. "Things started out friendly, but then it got weird..."
- Romance -10 to 10: Just Friends. "A friend will always be there for a kind word."
- Romance 10 to 25: Romantic Interest. "It's too early to tell, but there could definitely be something there!"
- Romance 25 to 50: Lovebirds. "A connection of curious hearts. This is shaping up to be a beautiful romance."
- Romance 50 to 100: Sweethearts. "The foundation of a strong friendship has forged a lasting love."
Friendship 60 to 100:
- Romance -100 to -50: It's Very complicated. "Aren't love and hate just two sides of the same coin?"
- Romance -50 to -10: It's Complicated. "The burning romantic desire cannot be quelled, even if they don't like each other that much."
- Romance -10 to 10: Just Good Friends. "This is a solid relationship built on trust and good memories."
- Romance 10 to 25: Romantic Interest. "It's too early to tell, but there could definitely be something there!"
- Romance 25 to 50: Lovebirds. "A connection of curious hearts. This is shaping up to be a beautiful romance."
- Romance 50 to 75: Lovebirds. "To be in love is a beautiful thing!"
- Romance 75 to 100: Soulmates. "Two Sims, one heart."