Emotional Distress

I have this lingering feeling na talaga of doing something to ease my mind. Alam kong hindi cheating partner yung kasama ko and he gave me permission to check his inbox. Napa-scroll naman ako and I still saw an existing conversation nila ng ex niya kaya tanong ko sa kanya why didn't he delete it. It was supposed to be a no big deal kaso the way he treated his ex was something he never did to me, like being understanding and doing things what his ex tells him to. Opposite yung sakin. I know mababaw pero hindi maalis sa isip ko na halos whole day umiiyak lang ako kasi I keep on asking myself na am I not deserving to have that kind of treatment. I'm 3 months pregnant, alam ko makakasama kay baby kaso hindi ko talaga mapigilan, I confronted my partner about this but he wasn't even helping, kahit assurance lang, wala. Minura pa ako. What should I do?