Girl asks to open relationship, boyfriend of 7 years turns her into the side chick

I am so jealous of my boyfriend's girlfriend.

My partner and I of seven years decided to be in an open relationship about a year ago. He stated he didn't want poly but really just s*x and fun connections and what not. Well he met someone and now he spends half his time with her. They go away for days at a time, I am forced to Google schedule time together otherwise he fills up his time with her, I don't feel like a priority. He says I am and I expressed that they are spending too much time together but it has seemed to fall on deaf ears. He had told me time and again if it came down to it he would chose me. While I didn't give him an ultimatum he told me a couple days ago that he won't break up with her and that if I cannot handle this new change in the relationship then essentially it will end. I am absolutely gutted. I feel like this is the beginning of the end. He said if at any point we need to shut it down we could but now he has changed his mind. He spends time with her family and goes away on little trips and runs when she calls crying and I feel like this is going to tear me apart. He is a good man but all I think now is that he is choosing someone else. If I don't put up with this then it's over. He knows I am upset and I can't help it. I feel like my anxiety and sadness over this will push him into her arms and home will not be a place he wants to be anymore. I feel like he bait and switched me and now I'm sharing the love of my life 50/50 without a choice. Less than that because our of the 50 percent he is at home, his work and friends and other life stuff needs to be addressed. It was my idea to open the relationship and I feel like I am losing him and I feel like I will lose him.