Most Helpful Guy
Frankly you can choose what you want to feel. You don't have to trust him. You can believe he's cheating. You can hate him for it. You can assume that you're the problem, or he's the problem. You can blame him, you can blame yourself.
I have some questions:
1. did you catch him in the act?
if so, did you ask him why? Did you let him try and tell you? Was this the first time this has happened? (If this has happened before I recommend you drop him).
2. are you assuming he's doing it because you snooped through his phone?
If you're snooping through his phone if anything he shouldn't trust you! Because you don't trust him! It needs to be mutual trust.
3. are you really giving him everything? Are you spending a lot of time with him, do you guys do romantic things, have lots of sex, make out a lot?
I'm not saying it's your fault, but you could be driving that horse. Pushing him away. However, if the answer to this question is yes, then I'd drop him because he has ulterior motives (like @Victorianne said).
Asking a forum really isn't the solution. Because there are a lot of biased opinions. People on here have gone through some things similar to this and can give you misdirection. Honestly, I'd ask yourself the questions I just asked, and figure out what you want. Get his side too. Keep an eye on him. If it continues then you need to ask yourself if you want to continue being with him. Trust doesn't break immediately, it's something that breaks overtime.
Most Helpful Girl
If he's sneaking around then he has ulterior motives. I wouldn't trust him. It's very disrespectful to behave that way when you are in a relationship. I can't be in a relationship with a guy who I can't trust.
I have boundaries within a relationship. If a guy crosses those boundaries... I end the relationship. I can be happy on my own , but I can't be happy with a guy who is disrespectful towards me , or with a guy I no longer trust