While Beatriz is away in Cartagéna, Armando is actually the only one to catch Betty on television by mere accident. Of course, guilt-ridden and heartbroken, he expresses that he's probably hallucinating, but there's no way they idea of it being real didn't cross his mind. Fast-forward to when Beatriz becomes president and wants to help other women get real help in accordance with their body instead of super-model standards, and Catalina comes to visit. Cata defends her idea from Hugo Lombardi by saying Betty's appearance changewas at large caused by her. Notice how Armando reacts in contrast to most everyone present, then think about why. He knows where Catalina was just recently, he remembers the night of the show, and he knows who was missing around that time-frame. That's the face of a man who was really close to putting two and two together.
The first time before Betty and Armando have sex, Armando is initially determined not to do this to Betty - not because he doesn't care about her, but the opposite: He doesn't want to hurt her. Then, after watching her break down, he makes up his mind to "lie" about loving her and go through with it. For the first time, two very dissonant tracks play over each other (one a slow, romantic piano ballad and the other the ominous confession music used throughout the series) without either being in the process of fading out. It's an intentional clash, because both the beautiful and horrible of the scene are happening at the same time: Betty feels an explosion of love and warmth inside her chest, all the while Armando is making one of the most difficult and potentially horrible decisions of his life by making love to a woman he thinks he doesn't love partly out of pity, and partly to save his company.
Even better; the love theme eventually overpowers the much darker music, because Armando did care about Betty, and their feelings did overpower everything else going on at the time. He let himself go completely, forgot why he was doing things...And what once was a lie, a nightmare, became a truth and a dream.
This kind of meshes with Fridge Brilliance, but one of the major reoccurring details of the series is Armando lying awake at night next to Marcela, replaying the words his father told him precisely about not being able to sleep because of your acts. This gets a payoff during the board of directors, but it's worth noting that the time Armando finds out about Beatriz' failed love life and feels true guilt over his actions for the first time, we get a nod to it. After Armando brings Betty home, there's a scene where the two sit in the car. Betty remarks that she's going to see him in her dreams all night. He remarks the same. Problem is...There's a much darker undertone. It's said romantically to her, but he's not just going to dream her because he loves her; he's going to dream her all night because he's going to be thinking about his acts, just like his father said.
Armando kicking Nicolás over and over outside Inés' house. He admitted later he couldn't stop once he started. He defended Betty against Marcela when she reproached him that Betty had slapped him - because had Betty not slapped him in defense of Nicolás, he would have kept kicking. He admitted to Marcela that he was so drunk and full of pent-up rage that he could have killed him. Nicolás could have died. Armando could have killed or at the very least left very seriously injured or crippled Betty's not just friend, but brother in all but blood. The entire romance of the two main characters would have fallen to pieces right then and there, alongside everything else.
It's also horrific that Marcela's jealousy was such that she was able to shrug this moment off and think it was an excuse. You should never defend your boyfriend in such a situation, even if you love him. If anything, Betty saved all of them.
Had Nicolás punched Armando in the stomach instead of the face when he visited the Pinzóns, he would have probably wound up in the ICU at the very least for the injury to the ribs he already had and didn't want to visit a medic for. That would have been pretty horrible to look at.
Had Marcela arrived just a bit later to the bar, Armando would have died. And Betty still would have had to go back to Ecomoda and be president; just that this time she'd have to face the death of Armando and would have had to put up with Marcela, who would absolutely blame his death on her.