my friend almost left his long term girlfriend over a woman he met online (she gaslit him to befriend me - I'm not joking)

I (25m) have been friends with this guy for over a decade and he has been with his girlfriend for around 6 years or so. They live in different cities and both go to college in their cities. They got into a little fight last weekend and she said she needed some space to herself for a few days so he was fucked up. He went on Instagram (I'm pretty sure it was Instagram) and matched with this 25F who was clearly in a manic episode. <br><br>Now, she gaslit him to the point where I had to step in to do some damage control because he was literally going to break up with his girlfriend for this fucking psycho. <br><br>It all started when he met her on that app and they started messaging. He said she was an attractive person, but he didn't want to get with her or anything - he just said she was interesting. She then started asking him about his relationship and he told her about how they were having problems. Bare in mind his girlfriend said that needed space so he was alone and vulnerable and in a state. <br><br>The 25F told him she had gone through a similar, painful break up in the past and that she understood how he felt. She then said they should just talk on voice call because texting was too long and tiresome and he agreed. <br><br>They talked on voice call for several hours in a row and he didn't say anything bad about his girlfriend, but somehow the conversation was mostly about her and their relationship. When he needed space, she would ask him to give her a second to compose herself, but he told her he was fine taking a break. <br><br>They talked for several hours and he felt better. Fast forward to 2 days ago, I got a random voice call from this number (I didn't have her number saved) and I hear "hey, is that (me's name)". I was confused so I asked who it was and she said she was the friend he met online. I was like wtf...how did you get my number??? And she said "oh, (friend's name) gave it to me". I asked how and she said she told him she needed to talk to his friend about their relationship and (friend's name) gave her my number. I was in shock, but didn't say anything, I just told her I was busy and needed to hang up. <br><br>He called me 20 minutes later and told me about his relationship and how they needed to break up and he needed space. He said that the 25F told him he needed to leave his girlfriend and that he was blinded by his love for her (his girlfriend) and that she had told him that his girlfriend was cheating on him for sure. <br><br>I was blinded by my anger and told him that I need to hang up and that (25F) was a fucking psycho, but he told me to stop and that I was defending his girlfriend for no reason. I was blinded by my anger, but then I started talking to him normally and he started to come to his senses. <br><br>I told him he needed to go back to his girlfriend and leave that fucking woman alone and also to stop speaking to her. He started to cry and come to his senses and then said that (25F) told him not to talk to his friends and that they would all be against him because they would defend his girlfriend. I then told him that I was not defending his girlfriend, but (25F) and that she was the problem. <br><br>He then blocked her number and deleted all the apps they were speaking on and he went back to his girlfriend. I'm just still in shock. Reddit, I just can't believe it. I'm still trying to process it.