Heartbroken- venting

How do I come to terms with this? I would have done anything for this man. I would have changed anything, fixed anything. But he couldn’t care less about giving us an ounce of effort for repair. He’d rather throw away a decade of marriage and find someone new a month later like I meant absolutely nothing to him. People have grieved the loss of a pet for longer. He acts like he didn’t promise to love me through the good and the bad, like he didn’t promise to take his last breath with me. Now I get to watch the man I dedicated my life to honoring fall in love with someone else. He’s making her laugh, he’s comforting her in the middle of the night when thunderstorms hit, he knows how she takes her coffee and he’s making love to her and looking into her eyes. Everyday he cares a little less about me, the mother of his children, the woman who spent a decade supporting him and his dreams and putting my own dreams aside to lift him up, and he cares a little more about her everyday. I can’t even look at another man and he’s in love with another woman. My heart is in a million pieces and I would do anything to put it back together even just a little bit. 6 months feels like a lifetime when everyday is so sad. I know I deserve better. I know if someone wants to leave your life, you let them. But it doesn’t make the pain any less. I’m exhausted, physically, mentally, emotionally. Why do some people feel the way I feel and others walk away without a scratch? Maybe I cared a lot more, or maybe I’m just an idiot.