At least once a day, I see people posting about one of the following scenarios:
1) asker suspects that his/her S/O is cheating and wants to know if it's okay to check the other person's phone, or
2) the asker checked his or her partner's phone and got caught; now, his/her partner is upset and the OP doesn't understand why because "if s/he loved me, s/he'd tell me everything".
The answer to both is a resounding no from me. And here's why:
I'm aware that this generation overshares via social media; it's become so normal that keeping anything to yourself these days seems "weird" and is automatically deemed a reason for suspicion. But surveillance in relationships is dangerous because it erodes trust and is a breeding ground for misunderstanding.
When you look at your partner's phone or social media accounts, you're only seeing one side of that person: you have a ton of data about your partner, in the form of Likes, dislikes, etc., with absolutely no context to any of it... So, if you go snooping to soothe your paranoia, chances are that whatever you find will have the opposite effect.
If you share absolutely everything, there's no mystery to keep you hooked. All the magic is gone, and the spark that keeps love alive over long periods of time will disappear.
When I was a kid, I lived in a small apartment and shared a bedroom with 3 siblings; I couldn't even keep a diary, for fear that someone would find it and read it. My thoughts and feelings weren't safe anywhere- I often wrote at school and carried my binder with me from class to class... Then, at the end of each day, I would take any poems or stories out and hide them in my locker, where only I could get to them.
As an adult, I'm a very private person. I have nothing to hide, but I like keeping things to myself... and, if some guy wanted to violate that to prove something, he'd be out the door. I don't owe you "proof" of anything. And, if you're going to insult me by implying that I can't be trusted, chances are you aren't someone I want to be with.
A few years back (well before Steam, Origin, or any of those existed), I preordered a game that I was super excited for... But it showed up just as I was getting ready for work. So I put it in my desk, still in the plastic wrapper, for me to play when I got home that night.
When I got home, my then-boyfriend was on his computer... playing my brand-new game. Not only had he taken something that wasn't his, but he'd gone through my desk to get to it and had the nerve to suggest that I was the crazy one for being upset.
We broke up not long after that. No surprises there, of course.
These days, my now-husband uses Chrome, meaning that he's logged into everything 24/7. This means that I have full access to his email, social media accounts, and everything on his computer... but I don't check them, nor will I ever.
Why? Because I trust him, and he's demonstrated that trustworthiness in ways that don't involve me violating his privacy. Likewise, I know he's not on my computer reading my poems/school assignments/terrible fanfiction- I share my work with him if and when I choose to.
So maybe your ex cheated and you have a hard time trusting the opposite sex. It's happened to me, and I've experienced firsthand what happens when you let a lack of trust destroy your relationship.
Nothing like starting a brand-new romance off on the right foot with a winning line like "I'm clingy and insecure, and I'm gonna violate your privacy until you prove you can be trusted, which is probably never". Or at least that's what it sounds like.
If you don't trust your partner, get out of that relationship. If you don't trust someone, you can't possibly love him (or her) and should quit while you're ahead.