So stressed- Please help!

A girl i know started to date a guy i know around the end of December, they rarely saw each other because of 'work'. I saw her around uni moping around for weeks, but he seemed really happy- like more happy than usual but i left it...

In January, she set her relationship status to seeing him, but he didn't do the same. I thought this was because it was kinda early on so i ignored it....

In the beginning of february she had liked every single fb post he put up, including all of his pictures and statuses, but he hasn't liked ANYTHING to do with her, but is on fb all the time liking other girls stuff. 2 of his best female friends refuse to add her on fb so i started to wonder why but i didn't comment.....

He didn't buy her anything for her birthday even though she got him something, and even 'forgot' it was her birthday even though it was all over fb.

His mum and 1 friend added her, and she added his mum and brother.

February 10th, he uploaded a status, basically saying he was 'finally' going to be 'riding' a really ugly girl that night- but something is better than nothing. So i was confused because i thought he really liked her- with adding family and stuff. But then i looked back on the last few weeks and realised how miserable she had been and all of the statuses of his that didn't make sense started to make sense.....they were all laughing about how gullible 'easy' and 'slutty' girls are. She and her mum have been blocked from all of these statuses, they don't appear on her feed, which i thought meant that they were about her but couldn't prove it. But then if they weren't about her- he's cheating?

I ignored this too (i know i probably shouldn't have but i really thought he liked her). He uploaded another status saying he was out drinking with her- but no kisses, of mention of 'gf and bf'. Then i saw her at uni 2 days later crying because he's asked her to remove her relationship status on fb. If i didn't know they were dating, i would deffo think he was single. He's even been very flirtatious with me and has liked some of my photos and statuses.

She has also uploaded 3 things to his wall which he has immediately removed. 1 of his friends posted on his wall asking who she was and he deleted that too.

Neither of them know that i know they are dating because he doesn't know that i know her....I found out through her friend.

what the hell do i say if she finds out i know him? If she asks if he likes her? I don't even know if he does or not. He's added her mum and 2 friends of hers (inc me), although he ignores her mum and other friend.

His friends openly mock her on fb, as does he, and blocks her from his posts. He's obviously trying to appear single on fb. But he's been 'with' her 4 months now and hasn't left her....but with them only seeing each other once or twice a week- for sex i might add- and have only been having sex for 2 months, i don't know....

I'm so lost. What do i tell her?
I'd want to know what i know if i were her but i just don't wanna get it wrong.

It's true that you know them (or at least claim to) but once they get serious about their relationship I don't think there's a lot you can do before you get accused of interfering.

Maybe you could show her his status and posts on your Facebook and infer he's bad news. Maybe you could gently suggest he's flirted with you or something? If your good mates with her, ask questions about the relationship, point out how it's not normal what he's doing. Or just lie- tell her u had a bf who did similar things he's doing and how you're soooo glad you dumped him cuz it's made you feel more free and know your worth