He won't stop lying!

My SO will lie to me about watching porn. And I tell him I won't get mad if he does. He's allowed to as long as it's in moderation. But apparently moderation is doing it more than what he's been telling me he's doing. Feel like I can't trust anything he says to me. I stayed with this man through a lot of stuff. Two months into our relationship he was diagnosed with cancer. I stayed with him through it all. I stayed with him when he didn't work. I stayed with him through the chemo and radiation and surgeries. I cook and clean for him. And what do I get? Lies. He messaged other women. Two whom were amateur pornstars paying for their porn and one whom he had a sexual relationship. I asked him why he did it. Idk. He always says idk. I ask him do you want to be single? Am I too much? I sit here and blame myself for his actions. Obviously I forgive too easily. I'm just at my wits end. He acts like he doesn't care and I'm sick of it. I deserve better than this. And he can't see what's in front of his lying face. And it hurts. It hurts so bad.

Edit: me and him both agreed that porn was affecting our sex life. So he cut back. Or so he says. He's allowed to masturbate and watch porn. Just as long as it's in moderation. I'm not his mom and I'm NOT trying to control him. I'm more upset about the lying.