I can't speak for other developers, but here's what I use:
1. 3D Models and scenes: A heavily-modded Koikatsu Party (available on Steam - make sure you check the Guides for how to install CharaStudio)
2. Coding: Ren'py (Visual Studio Code IDE)
3. Graphical editing/UI design: Affinity Photo
4. Video editing: Da Vinci Resolve
5. Music/Sound editing and creation: Audacity
Good luck making your game! I'm sure your boyfriend will be delighted :)