First guy sounds like he 'benched' your friend. Meaning he will have thought someone better came along and probably given them the valentines attention, may not have worked out with her, so has gone back to your mate who he put to one side just in case.
She needs to get rid.
I once had a guy dump me out of the blue after things going well and I got the gist he wanted me to beg for him back. I didn't.
So a few days later he went to 'sort out our issues'
and I went along with it.
Just so a week later I could dump him via a nasty text listing all his faults and 'issues'.
I'm very petty though