Trust

I love my boyfriend so much, and he's amazing to me, but I can't help but not trust him. I've found pics of other girls on his phone many times and have been sent questionable convos of him and a couple other girls. I feel like he hasn't been able to get over his ex gf. He saves convos saying no other girl can replace her ever.... Were going to have a baby together...that scares me! I don't know what to do.. He tells me he loves me and all that but it makes me sick that I can't trust him completely. I've messed up in the past myself and have changed completely. I know people do stupid things but it hurts especially since were expecting. June 27th I got std testing along with normal Pap smear and what not, it came back normal, when I went to the doctor in beginning of august and they told me I had an std... I hadn't slept with anyone else but him... He had it too. I let it go but it still bothers me:( I have no idea how it could have happened. I had the same thing when my ex cheated on me but that was 2 years ago. He told me it probably had just came back.....I'm at a loss of what to do ya know.