Q&A: Lovestruck

The ones from the Romance Skill are:

Introduction:
> Romantic Introduction (sim throws red petals)

Affection:
> Build Up Partner
> Emotionally Connect
> Share Sweetheart's Box... (requires shareable food (new chocolates/treats) in inventory)

Flirtation:
> Ask to Seductive Dance (trailer dance)
> Recap WooHoo (after woohoo has happened)
> Whisper about Desires

Physical Intimacy:
> Lovingly Dip Kiss (trailer dip kiss)
> Tender Neck Kiss
> Steamy Make Out (trailer make out)

Self-Interaction:
> Scan the Room (like Scope the Room in TS2, highlights attractive sims for a second)
> Aura of Flirtiness (makes surrounding sims Flirty to set the vibe or making romance easier)

Without Romance skill required:
> Ask to Wear Couples Costume (§100) (with costume chest on lot, both sims wear paired costumes)
> Ask to Wear Flirty Costume (§50) (with costume chest on lot, target sim wears costume)
> Compliment Form (on exercising sim, whilst at Gym)
> Cuddle in bed with... (on double beds)
> Goose (this only appeared for me with the Wholesome Romance Dynamic)
> Go to Sleep Cuddling (whilst cuddling in bed)
> Make Out in the Great Outdoors (whilst at the Park)
> Offer Seductive Dance to... or <sim> (on stereos)
> Present Romantic Gift... (pick gift from inventory, unavailable with no giftable items)
> Give Flowers... (requires single flower or a bouquet in inventory)
> Snuggle... (pick sim, on romantic blankets)
> Show Off Fitness (whilst at the Gym)
> Watch Sky with... or <sim> (on benches, picnic benches, romantic blankets)
> Wear Confident/Flirty/Playful Costume... (theme, outfit) (via costume chest, costs §50)
(note: Costume Chests only cost money on community lots, it's free at home. Likely a hiring fee)

There are also various non-romantic interactions around relationships, attractions, boundaries and non-romantic interactions on the blankets etc. Let me know if you want a list of those too.