Oh boy. Shitshow unfolding

My best friend has recently made a mistake that I made years ago. He’s dating his coworker, not only did that backfire, she’s an asshole (I mean that the nicest way possible). Ever since they’ve became a couple she’s treated me like I’m stupid and lies to my face about things that are obviously not true, and she’s very possessive. When I made a joke out loud to him, she had this look in her eye and threatened to kill me. She also makes jokes that really get me steaming mad and I think she knows that, so on top of all that she’s a bully. I can tell when she’s in the car with him because of how he talks to me. When she’s not he’s his normal self and when he calls me he says his normal “hey man!”. But when she’s with him and he calls me he says rude things, for example he called me to ask a question and she was with him and he addressed me by saying “hey fuckwad” in a nasty tone and she encourages the behavior. She also tries to hook me up with gay guys (I’m straight) because I’m thinking about getting a new car (a Subaru). He’s changing in a not good way and I think it’s because it’s his very first real relationship and he doesn’t want to lose her. It’s not my relationship to butt into but it’s starting to drive me insane. I don’t hangout with them in person anymore after the other night because she literally treats me like I’m stupid, although I know I’m not. I make up excuses to not go out with them. Also they’ve been together for 2.5 weeks now and they’ve never left each other’s side. She practically lives with him since the first day they’ve become a couple. I’ve been down the road with dating your coworkers, and having a very clingy and possessive girlfriend and both didn’t go well. I’m kind of watching from a far distance because I know it’s going to go downhill. She even got really mad when he told her he didn’t like Mac and cheese but ate it anyway to make her happy, she called him a liar over that. She always takes his phone when he’s talking to me so she can talk to me for 30+ minutes, and looks for my validation on things so I can take her side on topics. I’ve been nice about it, but I’m starting to get fed up because she’s fully possessing him. My mom is like his second mom and she tried to talk some sense into him, but he always says the same thing “it’s fine” in almost a dismissive way, like he’s silently saying he will do what he wants no matter what you say. I don’t like her at all because of all this. At first she seemed kind and friendly but that changed quickly. I don’t know if he notices it and is dealing with it because he’s grabbing on and won’t let go, or if he’s blinded by the attraction. Also by day 3 they were already saying “I love you” to each other. He’s 18 by the way and I’m 20. It’s probably just immaturity on his end. I’ve also been told I’m mentally more mature than a good amount of people my age, and I blame that on real world life experiences. Thanks for reading, if you want to drop a comment, you’re more than welcome! :)