advice on my marriage..

My husband and I have been married for 4 years together for 6. We just had our first baby back in December. 
He's our rainbow baby, and it took 3 years to finally get pregnant. 
The past month I've just been very annoyed with my husband. 
He's a great dad, helps with everything. 
And it helps that we have such a happy baby! 
I'm a stay at home mom, while he works until august when I start my job back. 
My husband has a history of cheating (once in the first year of our marriage we're over that) 
But he watches porn.. and knows I can't stand it. 
He's known this since day one. I constantly feel like I want to know if he's looking shit up or not. 
And he lets me go through his phone with out a fuss. Like he doesn't care if he gets caught but like it's a game if he can hide it so I can't find it. 
On google, Facebook, Pinterest, ifunny, YouTube. You name it he's looked there. 
But I always find it. 
I am so tired of not trusting him, and I always say one more time and I'm taking our son and leaving you. 
I left him for 4 months back when he cheated with his ex.. but haven't since. 
I'm tired of not believing him, and always second guessing myself with him
I want to leave but I really do love him and he's great with our son. 
And I don't want my son to have divorced parents like I did. 
So I feel like I'm stuck between a rock and a hard place. 
Any advice please. 
And I'm going to ignore the posts that porn is normal etc. in my religion lust is just looking at another woman much less a nude one.