Nude pics found up on my SO's computer

Colleen
Ok so my SO and I have been together for 4 years now. We live together. We have great sex and I think often 3+ times/week. I went on his computer NOT to snoop but simply because mine wasn't working. He had tumblr on and a picture of a nude girl (that oddly looked like me but obviously wasn't). The topic was "amateur nude mirror girls". I'm not upset but what does this mean??