Partner cheated..took him back..now paranoid as hell!

Cut long story short been with him for 7 years on and off..he already had a child of 3 when i met him..he cheated on me with his baby mum...we split up for 6months he came back i forgave...2 years later we started trying for a baby nothing was happening found out he got his baby mum pregnant again and has been living with her ( he was living a double life ) kept me a secret! Found this out in October 2016. He made out he had another kid with her cos she really wanted another full sibling for there son cos he was on his own...? So he felt blackmailed into it! So he says! Anyway i took him back again yes again!!! Cos i am desperate for a child of my own but i cannot get over what hos done to me i am so parnoid im always arguing with him and bringing it up then he gets angry. Im even having nightmares about them both together driving me insane. I just dont know what to do i love him but i cant get over it and i cant imagine being with anyone else now..