Ok this is going to be quite long winded and babbly (a word?) So apologies. Tbh I know the answer to all of this, I think I just want confirmation and a bit of support.
I started seeing my bf about 2 years ago. It was quite rocky as we had both got out of difficult relationships and were carrying a bit of baggage. Despite the ups and downs we both believed we were meant to be together so always ended up back with each other.
Then last Xmas my bf was supposed to spend it with me and my family but we fell out about a week before. He wasn't happy at the prospect of spending Xmas alone - understandably - and I received a text from him that didn't make sense. It was saying things like "let me come home, I'm sorry, we're better together" etc and a couple of specific things that didn't apply to me. I realised that it sounded like a text to his ex. I confronted him and he admitted that he had sent me the text on purpose to make me think he was texting her to make me jealous. Now I have no idea - still - if he did send it on purpose or if he was actually meaning to send it to her. He swore blind it was for me but I only have his word on that and all I do know is that I lost a lot of trust at that time.
We ended up back together and last weekend I stayed at his. We had a few drinks and were talking about our relationship and what kept going wrong and what we could do to fix things once and for all. We were both relaxed and were talking about trust issues between us and I suggested swapping phones as a sign of trust. I have no idea why I said it, I know looking at someone else's phone isn't the norm, I can only think that I was showing I had nothing to hide? Anyway his immediate reaction was NO! I was a bit taken aback because were were talking about trust and being open etc and I admitted I was a bit upset about it but it wasn't a huge thing and I wasn't going to get into a row about it.
So we carried on taking but he kept asking if I was annoyed and telling me his phone was his private property and even in a relationship you needed privacy and I shouldn't ask to see it and he shouldn't have to show me etc. At the same time as this he was scrolling through his phone and I could see him tapping and scrolling away 
After about half an hour he gave me his phone and said "there you go then". It was pretty obvious he had gone through his phone and deleted stuff so I wasn't interested in looking but when I told him this he got really annoyed and started saying I didn't trust him and he hadn't deleted anything and why didn't I believe him and why was I doing this etc. It got to the stage where a row was imminent so I said I was going to bed.
For the next hour he kept coming into the room, switching the light on and crying, saying again why are you doing this, why don't you believe me, I've done nothing wrong and you don't believe me and having a go at me for wanting to check his phone because that was private and people don't do that. At the same time he kept giving me his phone telling me to check it.
Eventually he calmed down a bit and we could talk normally so I told him that it was obvious he had deleted stuff and I hated that he was lying to me and and making me sound like I was mad for doubting him and I just needed honesty from him. He then finally admitted that he had deleted stuff but it was "just old photos". He said that he didn't want me seeing old photos in case I got upset but that's all it was.
(Can I point out at this time that he used to go swinging and is very open and adventurous when it comes to sex and likes taking pictures and videos...)
I asked him if he had old sex photos or videos of his ex but he denied it, he insisted it was just old normal photos.
Anyway, I was just glad he was honest, finally, but over the next few days I realised that any trust I had left was disappearing fast. As I said, we've had a rocky relationship and he has a habit of denying things, even when it's obvious. For example, he sends me an emoji every morning without fail but a few times he's been upset about something he hasn't sent it. It's completely obvious that he's upset when that happens and yet he'll still deny it. So denying things is a bit of a habit and I'm now in the position of having to trust someone who finds it very easy to not only lie to my face but to accuse me of not trusting or believing him when he knows he is lying.
As I said, it's clear this relationship is over, I guess I just needed to let it all out and get it straight in my head. Thanks for listening 