Eilert is all about being caught in between. He’s in between Hedda and Thea, aristocracy and life as an outcast, scholarly fame and shameful disrepute, drinking and not drinking, courage and cowardice. His role in Hedda Gabler revolves around the tension of being in between – the pressure to move in one direction or another.
Hedda doesn’t exactly help with the stress, either. In fact, she’s the main proponent of this back-and-forth action. We know she has jerked Eilert around before, sometime in the past when they were…dating? Sleeping together? Friends? What exactly WAS the situation with Eilert and Hedda? To figure it out, we have to do a fairly close reading of the dialogue, and make a few assumptions about what the subtext actually means. Take the nuanced conversation in Act II, the hints about Eilert's background in Act I, throw in a dash of Victorian background knowledge (see "Setting" and "Sex Rating" for specifics on interpreting these implicit statements), and we can conclude the following:
Eilert comes from a wealthy, aristocratic family. This is important to remember, because it puts him on the same level as Hedda and Brack, NOT in the middle class represented by George and his Aunt. All those references to his "past sins" refer to one thing: alcoholism. Eilert used to run around town getting drunk and hanging around with the wrong crowd, specifically Mademoiselle Diana, a prostitute of sorts. Hedda was intrigued by Eilert’s apparent disregard for the rules, and the two of them formed a friendship. Eilert used to visit Hedda, and the two would converse about all his unseemly activities while their chaperone, often Hedda’s father, sat across the room and out of hearing range (though able to keep an eye on them none the less).
Then Eilert wanted more – as far as we can tell, he wanted to have sex with Hedda. Hedda said no, and considers this refusal a mark of her cowardice. (She refused because it would be quite the scandal for the General’s daughter to end up with a debauched alcoholic.) Hedda also threatened to shoot Eilert but didn’t – she considers this the second mark of her cowardice (a.k.a. her fear of scandal).
What’s important to remember from all this is that Hedda likes Eilert as an alcoholic. She likes the idea that, for all the repression and restrictions of society, someone like Eilert still exists – a man who basically says "Screw you" to all the prim and proper tightwads of the upper class. Notice that Eilert is even cavalier about money – he won’t compete for the professorship because he "only wants to win in the eyes of the world." Hedda is all about this renegade character.Thea, on the other hand, is a totally different story. She likes Eilert as a reformed man – a scholar, a writer, and a teacher. It makes sense, then, that sparks will fly when the three of these guys end up in a room together. Keep this in mind: Hedda and Thea aren’t two jealous women fighting over who gets to have Eilert; they’re fighting over which man Eilert will be. As Hedda puts it, they’re fighting for "control" of his "destiny."
So what’s a poor Eilert to do? It seems that he chooses the conformist lifestyle alongside Mrs. Elvsted. Notice that, for all Hedda’s taunting, Eilert again and again refuses to drink. It’s not until his relationship with Thea is called into question that he falls right off that wagon. We realize that Eilert didn’t reform of his own accord. As Mrs. Elvsted says, she "got some kind of power […] over him." He gave up his drinking, she said, to make her happy. Eilert later confirms this himself: "I’ve lost all desire for that kind of life," he says of his former wild behavior. "It’s the courage and daring for life—that’s what she’s broken in me."
This raises an interesting point – the relationship between courage and drinking. We know Hedda thinks that Eilert is courageous when he’s drinking and cowardly when he’s not. But here it sounds like even Eilert feels the same way. He almost resents what is essentially his domestication on the part of Mrs. Elvsted. Look at his word choice: she’s "broken" his "courage" and his "daring." Does that sound positive to you?
Speaking of resentful, what on earth is going on with Eilert when he breaks up with Mrs. Elvsted? He seems almost cruel when he tells her, "From now on, we separate. […] I have no more use for you." Ouch. And that’s before he tells her that he’s ripped up their brain-child into a thousand pieces. Of course, Eilert will later explain his seemingly sadistic behavior to Hedda. He felt that, without the manuscript, he couldn’t be together with Thea anymore. Why? Was their bond limited to the realm of the intellectual and scholarly? Did they share other interests? Most importantly, does Eilert, or did he at any point, love Thea?