Gouki, um...this is your WIFE you're talking about, and she's out with FRIENDS and not you on VALENTINE'S DAY?!?
I think Surreal's being easy on you, but I am not: You got big trouble here, my friend.
Perhaps she's flattered by this other guy's attentions...but the fact that she continues to hang with them, and not you, is the biggest RED FLAG I ever heard of.
I think if I were you, I would arrange to join the festivities. Get to know this guy, and make your presence felt to him...and also watch how they interact.
And for God's sake, take the blinders off. I know, I know...you still trust her. Yep, that's what did me in with my wife...I couldn't see through the BS until it was too late.
As I see it, you're on VERY shaky ground and need very much to face some very rough possibilities.
I don't envy you. I'm sorry if I'm being harsh.

I hope you can pull it off... Todd