Hi all, I've posted this in /r/legaladvice but I figured I'd post here for more visibility.
My sister (US citizen) recently got married to a guy she met in Taiwan. After a 2 year long distance (and 6 month relationship in Taiwan), he finally came to the US this February and they got married in May to speed up the status of his citizenship and such.
However, over the last 6 months we've been seeing some red flags. He doesn't ever show care or interest in her when we're together i.e. PDA, feeding her at restaurants, holding open doors, anything gentlemanly that most guys do for the ones they love. Some may argue it might be a cultural or personality thing but I am very openly affectionate to my lady around them and thought it would be some kind of example he might follow. Especially since my sister really likes that kind of thing and always tried to be affectionate to him, which sometimes he rudely refuses. It's also her first real/serious relationship so she hasn't ever had someone be affectionate to her and he knows this.
There's nothing inherently wrong with the above but it was just something that everyone noticed in our family. He's always on his phone at family functions, takes lots of selfies without my sister, and just doesn't engage with our family. We've taken him on 3-4 big trips where he hasn't had to pay a dime, but he doesn't even say thank you or try to contribute in any way.
After seeing a couple more flags, another social media-saavy family member did some sleuthing yesterday and immediately described him as the quintessential "f-boy" looking for an easy way to his US citizenship as his next plan is to join the military, which would solidify his status here. Upon further research, we found a slew of promiscuous-type women among the 1000 he follows on IG. And most of his likes on IG are girls.
We all strongly believe he is just faking his marriage to my sister.
Grounds for annulment in California include
"Either spouse perpetrated a fraud to obtain the other party's consent to marriage. The fraud has to go to the heart, or essence, of the marriage. A good example would be when one spouse persuades the other to marry because of a secret desire to remain in the United States."
How do we go about this to protect out sister from being taken advantage of? What kind of proof do we need? Any guidance would be greatly appreciated.