Is watching porn addictive and does it affect us in negative ways? if so, would it affect us biologically or just psychologically, say through guilt?

Sometimes: For some people, watching porn is one of many aspects of their sexual expression. They are not driven toward it, although they may frequently enjoy it. For others, watching porn becomes a compulsive activity which is addictive in nature and accompanied by guilt. While experienced psychologically, some evidence suggests that addiction is biologically based. However, this is not clear cut.