Example (not as devious as it sounds), my fiancee had this friend when we started seeing each other.
Rather than say she can’t go out with her, I encouraged it. She’d come to me after a night out with stories about her friend and how she did this and that and also that she didn’t agree with how she did this or that. Women love the gossip. So, she continues dishing the dirt on her friend, how she lead this guy on, made him buy drinks for her all night then went home with another guy and I am just nodding the whole time. All the time acknowledging that this behaviour is reprehensible.
Then there is the inevitable relationship fight, we argued, she gets on the phone to her friend saying he’s a big meanie, etc. They go out for a girls night. You now have ammo.
She comes home and I confront her, saying I know what her friend’s like and I think she is a bad influence on her and I can’t be sure that after our argument that she remained faithful. She has nothing to say, she knows it, she has bitched about it for months. Now, if she went and cheated on me that night, good, game fucking over (I have a great network, I’d know in minutes), except for the obvious break up sex that she doesn’t know she is having until after. If she didn’t cheat, she knows you have the upper hand, because she might as well have cheated, according to her own logic.
Now she starts to second guess the friends motivations, I offer stability. Her friend wants to go out and be hit on by guys, I want to go out with my partner and enjoy each others company. Her friend starts saying shit like, “you never come out anymore”, gf thinks, “we went out the past three weeks in a row, why is she saying this shit?”. Her friend begins to get nasty, saying I’m taking up all her time, that I am bad for her. But I am doing things like organising trips to the zoo, picnics, all those romantic gestures chicks dig. gf realises that going out with a slut is not helping her reputation.
GF decides to break ties, all off her own realisations, nudged only slightly by me. She does so in spectacular fashion, whereby I comfort and ask why? Why did this happen? You were such good friends.
And then she is trapped, soon to be my wife.
Just remember, I am also trapped. Trapped by my own strategy.
Stay single as long as you can, dude, trust me.