Boyfriend lied about female friend

Hi guys, I could really use some advice about a situation that just came to light with my boyfriend. It’s a little long of a post but I really need opinions of what to do here. A little backstory first is that we have been together almost 6 months and he has been nothing but amazing this entire time. I was diagnosed with epilepsy 3 weeks after we officially started dating and I’ve had a whole mound of health issues and doctor appointments etc and he has supported me through all of it and has put up with all my different mood swings and irritability that I’ve been experiencing from new medications. I also have a 2 year old daughter who is not his but he has stepped up to the plate tremendously with her and they both really love each other. So now to the issue at hand. A couple of weeks ago he was planning to come over and hangout with my daughter and I for the day and have dinner together. We had this planned for about a week but he called me the night before and said that he was going to have to leave earlier in the afternoon and not stay for dinner or anything because some of his old friends from high school texted their group chat and all wanted to have a bonfire and catch up and it was going to be at his house. I was slightly disappointed that our plans got changed but I totally understood that he wanted to hangout with his friends so I was ok with it. I casually asked him if this one friend of his was going to be at the bonfire (we’ll call her “Ashley”). He said he didn’t think so cause she probably had work. I would have been fine either way if she was there but I was just curious because he used to have a big crush on her in high school (which he admitted to me) and sometimes their dynamic / relationship just makes me feel a little uncomfortable or insecure. So he comes over the next day and hangs out for like 2 hours and when he was getting ready to leave I had a big seizure but he told my mom to tell me he was sorry but he had to leave cause he needed to get home for his friends. Ok that’s fine even though when I came out of my seizure I was very confused and upset and didn’t know where he was which sucked. That night he calls me to tell me good night and I asked him who all was at the bonfire and he said just a few guy friends and told me their names and when I asked what they talked about he gave me some weird generic answer like “just guy stuff” which struck me as a bit odd and seemed like he was just trying to avoid telling me details about the bonfire. I also asked again if “Ashley” came and he said no. So flash forward a few weeks and things have been fairly normal with us but I kept getting a weird feeling / vibe about him and his friend Ashley and about that whole night of the bonfire. Well he spent the night this past Friday and I know I should not have done this and it was a big violation of his privacy but I looked at his phone (he has given me the password). I looked at his Snapchat conversations with Ashley and saw that the week of the bonfire they were making plans to hangout (no mention of any other friends hanging out too). He outright told her he was completely free on the day he and I planned to hangout and so then the two of them made plans to hangout together and have a bonfire at his house, just the two of them. There were also a couple of sorta of flirty messages where he texted her sweet dreams with some hearts and she did the same back so that made me uncomfortable. So after I read this I was feeling really confused and upset and thought maybe he and I had a miscommunication and wanted to give him the chance to tell me that Ashley was at the bonfire that night and that no one else was there. I asked him casually when he last hung out with her and he said it had been a few months. I said so she wasn’t at the bonfire and he seemed a bit flustered and said “oh actually she stopped by for just a bit before work”. I said ok and left it at that and waited to see if he would open up and tell me more of what actually happened but he never did. All yesterday I had no clue what to do or if I should bring this up to him but today I decided to call him and just be honest that I looked at his phone and apologize for that but ask why he lied about a group of his friends hanging out when in reality it was just he and Ashley. Before I did this though I gave him one last chance and asked him outright if it was just the two of them at the bonfire that night and he again got a little flustered but told me no other people where there. So once I told him I knew that wasn’t true he said you’re right it was just the two of us and no one else was ever going to be there. I asked why he lied and he said his ex used to be very toxic about him hanging out with female friends and he didn’t know how I would react so he just lied about it. I told him I would not have been upset about them hanging out together but it really hurts me that he lied about the whole thing to me and made up a very elaborate story that was never true, and that he basically canceled our plans together and left me in the middle of a seizure just to hangout with her. I asked if they did anything inappropriate together and he said no but I don’t know if I should completely believe that or not. He then just apologized and said it was in the past and he didn’t know what else he could do to fix it now. I told him I loved him but needed time to process this. Sorry for this extremely long post but I really need advice on how to move past this or what I should do! Thanks 😓