Am I overthinking or is he hiding something?

This is a long one. A little back story. I have had severe anxiety for as long as I can remember. I have anxiety and panic attacks and have also taken medication for this and depression for as long as I can remember. As of the last 6 months I have been off my prescribed anxiety/ depression meds (drs request) while my boyfriend be I are trying to conceive. (We are in our late 20’s) In the mean time I’ve been taking Methylofolate (nurse recommended at therapy) for some sort of anxiety/ depression relief during this time. It helps a little but not as much as the prescribed medication I used to take. But I’ll do what I need to do for us to get pregnant and have a baby. Anyways, my boyfriend and I had talked for 7-8 months before meeting in person (we met on a dating app) we saw eachother in person a hand full of times over a few months before we decided he come live with me (he moved a whole state, left his family/ friends and quit his good paying job to come be with me. His whole life changed. It’ll be 1 year living together in a couple months. After the first 4 months or so of living together I bought a house where we share the expenses and the responsibilities. I have a 5 year old son that he has taken in as his own, they love each other to death. He also takes some of the responsibilities for caring for my son. We never argue, if we disagree, we agree that we are different people with our own options and outlooks on things and we are okay with that. We are very supportive of each other in every way possible, we communicate everything that upsets us and work through things together. Did I mention we are engaged? He proposed to me a few months into living in our new house. We love each other to death and wouldn’t have it any other way. My period is due tomorrow and the past 1-2 weeks I have been symptomatic (I have pmdd) emotional, crying, stressed out, (I was really hoping I was pregnant this time but with the symptoms I’ve had the last few days I really think I’m getting my period) my boobs have hurt intensely since I started ovulating, etc. I’m a mess from physical pain to emotional outbursts. Last night my boyfriend and I were messing around, and not in a sexy way, we were tickling each other and laughing and just playing around after my son went to bed. All of a sudden, his Apple Watch goes off with a message from a number that isn’t saved in his phone and a picture is attached. We were still playing around so when I saw it I kinda grabbed his arm and tried to look at his watch. (I’m very paranoid and every relationship before my fiancé, I had been cheated on, abused, gaslighted, neglected, I was raped once, they’d be talking/ flirting with other girls either behind my back or openly via text. So I’m very anxious/ paranoid that it’ll happen again especially after everything we have built together and the relationship between him and my son. I’m scared things will be ruined or I’ll start from the bottom again and lose everything I love.) Anyways, sorry for rambling I hope you’re able to follow along. I asked him who the message was from and he said it was probably his grandma but I said it wasn’t your grandma, your grandma is in your phone as grandma and I said it had a picture with it. I didn’t get a good look at it but my paranoid, anxiety ridden mind instantly thought it was of someone’s skin. It was just that color. But it could have been anything I guess, wood, a table, counter top. Anything idk. But I started panicking and he said “you can look through my phone all you want anytime you want, I don’t have anything to hide.” I said “I don’t want to look through your phone, I would rather talk about it so we can keep the trust between us bc the second I look through his phone, I feel like all trust will be lost on both parts. I don’t WANT to look through his phone. I WANT to feel like I can trust him. (If you haven’t guessed by now, yes I have massive trust issues) so I said “can we look at the message together to ease my mind?” He got up and walked to the tv and shut it off. I asked him “you don’t want to watch your show anymore? He said “I don’t feel like it anymore” I said “can we look at the message together?” He said “we just talked about this” I said “okay” and went to the bathroom to try to process what was going on. When I came out he was in the bedroom, I locked the front door and the door is kinda loud so when I did he came out worried and thought I was leaving. “I had just started crying and said “no” he saw me crying and we stood only inches away from each other. He took my hands in his and looked me in my tears filled eyes and told me I’m the only one for him, there is no one else, he loves me more than anything in the world, and he changed his whole life to be here with me and he wouldn’t do anything to ruin that. That he loves me so much and only me. I told him I love him so much too and I just can’t help the way my mind jumps to those conclusions because that’s all I’ve ever known. He asked me to come to bed with him and so we did, I laid there in his arms sobbing. He continued to reassume me there is no one else for him, he’s not the kind of guy to do things like that and he wouldn’t do anything to ruin what we have because he loves me so much and couldn’t imagine life with anyone else. But i still can’t help but think he’s hiding something. Am I over thinking or could there be something he’s hiding? He said similar things to me when I heard his phone ringing from a call from a girl on Facebook messager after midnight. I told him some girl was calling and he said it’s probably his buddy trying to contact him through his girlfriend’s account. But I’m still iffy on that one too. I don’t understand it. After I fell asleep last night I had a horrific nightmare that I was being raped and murdered in front of my family and son. Am I over reacting by thinking he’s hiding something? My anxiety is overwhelming me and I’m not okay. Maybe it’s just my period symptoms or lack of proper medication? What are your thoughts?