We still don't know much about the time frame between the end of Jack (Milo Ventimiglia) and Rebecca's (Mandy Moore) marriage and the start of her relationship with Miguel (Jon Huertas). It seems unlikely that Jack and Rebecca were divorced — their marriage has its troubles, as any relationship does, but it's built on love. Plus, in an interview with EW earlier this month, This Is Us creator Dan Fogelman suggested that Rebecca and Miguel's relationship started after Jack's death.
So how, exactly, did Miguel go from being Rebecca's husband's best friend to, well, her husband? According to Redditor harmony30, Rebecca and Miguel probably bonded over Jack's death. The theory, which Bustle discovered on the This Is Us subreddit, explains that the pair likely didn't have feelings for each other before they were left coping with their loss together.
"I think Miguel and Rebecca eventually came together because of their love and respect for Jack," harmony30 explains. "Even till today, Miguel speaks so highly of Jack... He misses his best friend just as much as Rebecca misses her husband."
Grief can bring people together, and Rebecca and Miguel were two of the most important people in Jack's life. So it's totally believable they would have developed a relationship over time if they spent more time together after Jack died. It's sweet, if not completely heartbreaking.