I 20F can’t decide if I think my boyfriend 20M watching porn was cheating. Any advice?

I can’t decide if my boyfriend watching porn and hiding it from me was cheating or not. This happened a few months ago, but I still think about it sometimes. He never told me, he only confessed after I found it on his phone. He was very apologetic, but it still hurts that we was doing that for years and I never knew. My mind flip flops between if it was cheating or not, especially because we’re so young. I love him, and I don’t plan on ending our relationship over this, but I’d like some guidance.