The Groom of Gallagher Mansion is a visual novel with 4 endings, and the ending you achieve is based on a points system that is rewarded in certain choices. Below is a spoiler-free walkthrough on how to get each ending in the game.

For The Truth

1. Lyreflowers
2. Investigate the Study
3. Necklace

For Love

1. Roses
2. Investigate Upstairs
3. Ring

For Science

1. Zinnias
2. Investigate the Dining Room
3. Earrings

Forever

Pick any combination of the choices above, such that you do not achieve 3 points towards any particular ending.