'Afterwards I told my girlfriend about it and she got furious at me': BF contacts GF's estranged sister to buy her an extremely expensive present

After one guy went behind his GF's back, and his big purchase began tearing this couple apart. When it comes to pushing boundaries in a relationship, this dude majorly messed up. In a post to r/AmItheA*****, u/throwaway84200t wrote that his GF doesn't speak to her sister. She hasn't told him exactly why, but they had not talked in four years. Then the OP began talking to her sister — apparently under the guise of trying to get the two sisters back in touch. But then this post goes off the rails. The OP apparently bought his GF's estranged sister a huge gift. He didn't even consult his GF first! Commenters, of course, called this guy TA for ignoring what his GF said. Some also noted that it seems like maybe OP is lying. What if he and the sister were actually closer than he let on. Maybe they're cheating together or are in some other way involved. It's strange that he would suddenly blow so much money on a random stranger! There's no way this guy will still be with his GF after this. Up next, this guy's HR was completely ignoring him, so he cued up some malicious compliance to get his proper salary.