@Ck123,
Ck123 wrote:
....
He doesn't know I check his phone ...
This is a complete headache.
It's going to become a far bigger headache if he finds out you have been checking his phone behind his back. It implies a lack of trust at the very least.
You will probably not like the consequences very much if you are caught. And this trust issue implies deeper problems with your relationship than you are letting on.
Talk to him now. Talk about how this all makes you feel and go to couples counseling if you feel it would help (or go alone if he won't go). Counseling is a far healthier solution than keeping this stuff locked away inside you.
And consider cutting your losses, too. You are not married; it is less of a financial headache if nothing else. Consider that the inertia in not wanting to leave a relationship can only get worse over time. Weigh it - and that can mean the old exercise of taking a sheet of paper, drawing a vertical line down the middle and listing pros on one side and cons on the other.