Great choice — Sri Lanka has beautiful, varied beach destinations that make romantic honeymoon spots. Below are top beach-side honeymoon getaways, with what makes each special, couple-friendly activities, and the best time to visit each coast.

1. Mirissa (south coast)

• Why go: Intimate crescent beach, calm swimming, famous for whale- and dolphin-watching excursions and sunset drinks.
• Couple activities: Private whale-watching boat, seafood dinners on the beach, short trips to nearby Weligama for surf lessons.
• Best time: December–April for calm seas and good visibility for whale watching. (funsuntravel.com)

2. Unawatuna & Galle Fort (south coast)

• Why go: Classic palm-fringed beach (Unawatuna) plus the romantic, historic Galle Fort — easy mix of beach, boutique hotels and colonial charm.
• Couple activities: Strolls inside Galle Fort, sunset at the ramparts, snorkeling, spa days at boutique resorts.
• Best time: December–April (dry, swim-friendly). (lonelyplanet.com)

3. Bentota (southwest coast)

• Why go: Wider resort strip with luxury hotels, river cruises on the Bentota River, and water-sport options — good if you want resort comforts plus beach time.
• Couple activities: Private boat/river safari, Ayurveda spa treatments, jet-skiing or calm beach days.
• Best time: December–April. (hayesandjarvis.co.uk)

4. Tangalle (southern coast, quieter)

• Why go: More secluded, long beaches with fewer crowds — excellent if you want privacy and upscale beachfront resorts.
• Couple activities: Long beach walks, snorkeling at quiet coves, wildlife day trips (nearby parks).
• Best time: December–April; however many find Tangalle quieter year-round compared with Mirissa/Unawatuna. (loxiastudiohotels.com)

5. Hiriketiya (Dikwella) / Dikwella bay (south coast)

• Why go: A small horseshoe bay popular with couples and boutique surf-yoga retreats — stylish but low-key.
• Couple activities: Gentle surfing, yoga classes, café culture and intimate beachfront dinners.
• Best time: December–April. (funsuntravel.com)

6. Arugam Bay (east coast) — for active couples who surf

• Why go: World-class surf break, laid-back vibe, good for adventurous couples who want surf, beach bars and a boho feel.
• Couple activities: Surfing lessons, lagoon safaris, cozy beachside bungalows.
• Best time: May–September (east-coast high season / surf season). Note: check current local security advisories before travel if planning to visit. (nichevoyager.com)

7. Pasikudah / Kalkudah & Nilaveli / Pigeon Island (east coast) — shallow, calm waters

• Why go: Long shallow bays with turquoise water and great snorkeling — very romantic for lazy beach days and swimming far off the shore.
• Couple activities: Snorkeling, glass-bottom boats, island boat trips and seaside dining.
• Best time: May–September. (nichevoyager.com)

Quick planning notes (important)

• Seasonal split: Sri Lanka’s weather is governed by two monsoons — the southwest/southern coast is best December–April, while the east coast is best May–September. If you plan to combine coasts, consider shoulder months (March–April or September–October) but expect some unpredictability. (lonelyplanet.com)
• Typical honeymoon length: Many couples do 7–14 days, combining a few days in the hill country (tea country/Ella) or a short safari with 4–7 days at a beach resort. (Brides.com)
• Security & practical checks: Check current travel advisories and local updates (safety, weather or any temporary advisories) shortly before booking or departure. Recent events have occasionally affected some coastal areas; always verify current conditions. (theguardian.com)

If you want, I can:

• Suggest a 7–10 day honeymoon itinerary combining beaches + one other region (tea country or safari).
• Recommend a short list of highly rated romantic hotels/resorts in any of the destinations above and sample budgets.