How long is too long to feel sad?

Jan 1st, the love of my life, whom Ive loved for more than 10 years, found the courage to ask for a divorce. He’s been unhappy for many years but felt too guilty to leave. I know he loves me and says I’m his soul mate. We were together for 5 months and had just gotten back from my niece’s wedding (he posed for family photos with me-we planned to get married eventually), and the next morning, out of the blue, he said he couldnt stand the guilt and wanted to give his marriage yet another chance. I was devastated and went a little crazy. Anyway, I know I decide what I want to think & feel, but I also know it’s natural to be sad and grieve this huge loss. I don’t know how to handle this situation. Do I continue to feel my feelings or do I choose to think things like “It wasnt meant to be” in order to feel better. Any suggestions? Thanks.