.. Reasons Your Partner Is distant

Question: Partner & I have been together 3 & a half yrs now, and were currently 7 months pregnant .. but since finding out he has turned into this person I don't even know any more , his so distant always has excuses not to be around hangs out with this girl who I've told him I dint feel comfortable with but he insists that they are just friends... long story short I've found messages from the 2 saying that they like each other & that they miss each other & their always thinking of one another .. & when I confronted him he says ohh babe I was just playing around its a joke mind you his got her name under hotness in his ph too and that was a big joke also app .. then he tells me his going to work & I find out that he hadn't been to work at all that week & when I confronted the both of them he was so blazae about nit cal & got angry with me saying I just came to get her bag & in gotta drop here off thats what we're doing now but you told me earlier that day that you were to busy to talk to me coz you were working .. so how'd you fit time in to see her ? only reason I knew he wasn't at work is I had an anti natal app that morning around the corner & spotted his car on my way there .. tried calling no answer knew something Was up told him in a msg it was urgent plz pick up but nothing.. I waited there for almost 2 hrs for him to come back to his car .. msgs me obviously after they were doing what ever saying can't talk ate the depo (His work) will be home in a few hrs ) lol but i9 cant get the look on his face outta my head it was as if he was disgusted with me for interrupting him .. then when I reminded him we had an antinatal app that he promised that he'd come to he turned around and said no I'm busy I've gotta drop her off only stopped in here quickly to pick it up .. I felt so gutted esp that he said that infront of her made me feel like I was worthless.. I've asked her to stop msg him also won't reply but when said to her face she said ok but yet still msgs him. every day babe this & babe that.. Mind you this is the same girl who's house he fell asleep at in her bed .. on the days we were supposed to get our first lil family photoshoot done but took her to work with him instead & then went straight back to hers and fell asleep in its bed .. every single day its a new lie to me so he can go and hang out with her .. am I being to possessive here or paranoid cox I don't think iam at all but he thinks I need to calm down & relax coz my hormones are all out of wack and I'm winding myself up over nothing coz he doesn't know why he said those things to her coz he doesn't want her he wants me he recon ... but when I ask to use his ph he gets all defensive and says what you wanna do ill show you & always deletes their messages after promising that he wouldn't coz he had noithng to hide apparently but when I try and talk abiout anything with him he Geta angry or makes up excuses like his tired ior busy even pretends to fall asleep with his ph gripped in his hand or in his pocket & lays on that side .. the list goes on and on but I just want to know why won't he just tell me instead of showing me what he wants coz his actions are the total opposite to what he says too me