If you're going to tell people to look into the lens of romantic*/companionate (and all the other ones you didn't mention: nonlove/liking/infatuation/empty love/fatuous love/consummate love) you should at least give them some starting points.

• Triangle theory of love: Robert Sternberg (1987, 2006)
• Brain regions; attachment/commitment vs sexual desire: Diamond (2004), Aron et al. (2005), Xu e al. (2011)
• Lust/attraction/attachment, dopamine/serotonin influences: Helen Fisher (2006), Aron et al. (2008),
• More influence of dopamine/serotonin: Ackerman (1994, p. 165)
• Critiques of simplifying love: Fehr (2006)
• Some more neurotransmitters and hormones: Macdonald & Macdonald (2010), Hill et al. (2009), Gouin et al. (2010), Ditzen et al. (2009), Theodoridou et al. (2009)
• Loves sternberg didn't consider: Berscheid (2010), John alan lee (1988),
• Decreases in romantic love: sprecher & regan (1998), Tucker & aron (1993), Gupta & Singh (1982) and the followup D. Myers (1993), Walster & Walster (1978), Abhmetoglu et al (2010), Call et al. (1995), Klussman (2002)
• Non-decreases in love: Acevedo et al. (2011),

Personally, I would really, really recommend the textbook Intimate Relationships by Rowland S. Miller to anyone who is curious about the subject. I had to go pull my edition off of the bookshelf to quickly throw out all the references above.

*because passionate love isn't the category. The proposed idea was the triangle theory of intimacy, passion, and commitment, which led to the eight above categories----