Agape and Eros are synonyms actually.

We keep hearing it declared that the Greek Language had multiple mutually exclusive words for "Love", the big three being Eros (Sexual and Romantic Love), Agape (Familial Love) and Philia/Phileo (Brotherly Love, which you're supposed to have for everyone).  From theologians like the late Karl Bart to to C.S. Lewis to YouTube videos like the Overly Sarcastic Productions summary of Eros and Psyche (a story that originated in the 2nd Century AD BTW).

The thing is, there is a lot of context about the history of the Language being left out of that.  I don't know if that's an accurate representation of how people in modern Greece use these words, but there are some important facts about the Ancient usage I need to point out.

First of all, and this is semi-well known, "Eros" is suspiciously missing from The New Testament, the closest we get is one guy's name seems to have Eros as one of it's roots, (Erastus mentioned in Acts 19:22, Romans 16:23 and 2 Timothy 4:20).

A popular theory for why is that the first Generation of Christians were a bunch of prudes seeking to reject Sex and Marriage so they had no need to discus Eros.  Well this entire Blog is partly dedicated to refuting that notion.

It's also been proposed that these early Jewish Monotheists wanted to avoid saying "Eros" because it was also the name of a Greek god.  Thing is lots of Greek words in the New Testament are also names of Greek gods, from Ouranos to Hades to some Olympians being explicitly mentioned.  But maybe there are nuanced reasons why Eros would be different, after all twice the Epistle known as 1 John says that "God is Love (Agape)".  Also not every deity in Greek mythology had an active cult of worship, most primordial deities were not as active as part of Greek pagan religion as Eros was.

But wait, why isn't there a Greek god named Agape?  A lot of abstract concepts and emotions are personified in Greek mythology, even some pretty trivial ones.  Well you see the well known academically but not so casually well known fact is that Agape is a word that was almost never used by Greek speaking Polytheists.  Apparently Homer used a form of it but not in any way comparable to it's NT usage.

In other words, Eros and Agape are a bit like Clark Kent and Superman, you kind of never see them in the same place at the same time.

The first problem with excluding Romantic and Sexual Love from the meaning of Agape is that Paul uses Agape of the Love that Husbands are supposed to have for their Wives in Ephesians 5.

But then there is the Septuagint, the ancient Greek translation of the Hebrew Bible.  As I've said before in my view the Septuagint is at least partly Pre-Christian in origin but the final from we typically know was copied and preserved through Christian hands.  Both Eros and Agape are used in the Septuagint, but Eros far more rarely.  It is the main place you find both being used.

Both words are used to translate the same Hebrew word, Ahav and other forms of Ahav like Ahavah.  But Eros is NEVER used in The Song of Songs that is Solomon's.  That's right, the most explicitly Erotic part of the entire Bible used Agape and not Eros.

I can't help but wonder if Agape might actually be Hebrew in origin.  There is a rarely used synonym for Ahav that only appears in Jeremiah 4:30, and Ezekiel 23&33, Agab, Egeb and Agabah (Strongs Numbers 5689-5691).  For whatever weird reason, Bs sometimes change to Ps in ancient transliterations, so Agape could easily have come from this word.  Some of it's uses do seem to imply a Sexual sense.  The Strongs definitions for the words say things like Sensually and Amorousness.  However I lack a smoking gun on this theory since I can't find a place where this word became Agape in the Septuagint, in the Jeremiah verse it is translated Eros.

So Agape can definitely include Romantic and Sexual Love in ancient Judeo-Christian use.

Meanwhile Eros was definitely used by Gentile Greeks of more then just Sexual Love.  Plato is someone who's attitudes towards sex I've strongly opposed on this Blog, but he is a witness to how the word was used, and Platonic Love was indeed Platonic Eros.  However what we today means be "Platonic" doesn't always match what Plato actually meant, so it's complicated.

So when 1 John 4:7 says that "everyone who loves is born of God and knows God" using Agape.  You can't say that's separate from the Love Homosexuals feel because of some modern notion of Agape and Eros being distinct.  Agape is used in negative senses sometimes, but that's only when Love for some thing gets in the way of one's Love for God.  It's never used of love for people.  Sexual Love can be sinful when it is expressed or taken against someone's will.  But calling any consensual romantic love Demonic is in my view potentially Blasphemy against the Holy Spirit.

Update: So I recently learned of a minor Greek Goddess called Philotes, she was associated with both Friendship and Sex, so that right there is evidence that Philia wasn't completely divorced from Sexual connotations either.