What's Next ?????!!!!

I don't know what to do at this point. I feel like my wheels are spinning but I'm getting nowhere. 

When I do my best to be " nice and sweet " to him it doesn't seem to matter because he always manages to find something to criticize me about ! There's always " something " that I did WRONG in his eyes !.... no matter if I truly didn't do a damn thing wrong... in reality ! It's always " his reality " that matters more than anything else ! 

Like just recently when I found a post on his facebook page from a recent ex-gf that he had swore to me that he had NOTHING more to do with; that he definitely did NOT talk to her anymore ! BULLSHIT ! 

Obviously he must have been talking to her. Why else would she suddenly post a " lovey-dovey " post on his facebook page that clearly implies that she wants him back !?! 

Of course when I calmly came out and asked him about it he completely denied everything ! He claimed that she didn't send the post - which was his first lie - and then he swore that she definitely does NOT want him back because she's in a relationship right now. I don't believe that for a second ! Even if it's true, obviously it doesn't matter to her since it's obvious that she's trying to worm her way back into his life. I would confront him again about this, but I know it wouldn't do me a damn bit of good. He's a master liar ! 

I've bent over backwards to do everything I'm able to in order to make him happy, but none of it seems to matter to him.... at least not if he's been flirting with this ex-gf behind my back ever since we got back together again - ( December 5 th, 2017 ). 

I want to believe him... but HOW ??????    

How can you believe and put your complete trust in someone when ALL of their actions point to deceit, and lies ?!?!?