I posted this in chat Tuesday when it happened and was told about this Topic so thought I'd vent/ maybe get some advice if that's ok , bare with me it may be long 
I have been with my Partner for 3 years this month , we weren't living together but were sorting all the logistics out to do so iyswim
Anyway I'm 8 weeks pregnant as we were starting a family hence the moving in together .
I sussed something was 'off' Tuesday as he had said a family member had been taken ill & having not heard from him I checked his sisters Facebook to see if everything was ok at which point I noticed on a status it looked like she were talking to herself 
the penny kinda dropped then so I went on a different Facebook and their he was on an account he said he didn't have with his arm round some woman all happy and smiley gazing at each other 
, I still couldn't get hold of him and had sent various texts etc & when I heard from him he didnt even bother to deny it just said he didn't know why 
wouldn't answer any questions and really hasn't said much since then .
I found out today that she and her son have been staying at his since Friday playing happy families - pictures at the beach and lots of status' about having had a great time and finally found that special somebody and she is the best girlfriend ever 
After some digging nosing about on facebook I found out they met on new years day this year yet he told me he couldn't spend the day with me as he was spending time with his Grandad as he was dying & completely ignored my birthday & valentines not that I'm bothered but its the thought iyswim anyway I've gone from been upset and now I'm rather erm volatile/angry
he is coming round tonight to see me so we can talk as he 'loves me' when quite frankly I don't think he would have even answered the phone to me if I weren't carrying his baby
I dunno what to do or what to feel or what to say