First I will say that it is perfectly natural to check out other people. If you are not a homosexual it is natural to check out the opposite sex. It is also natural to check out the same sex, and compare yourself to them.
If you are in a committed relationship, and your woman catches you checking out other women, then it may make her feel insecure about herself. Same goes for if she catches you looking at porn. Women are emotional creatures.
In committed relationships most women need to be made to feel secure about themselves and the relationship through the words and actions of their man. However, the levels of tolerance for such things varies from woman to woman. Some women are secure enough about themselves and their relationship so that when they do catch their man doing such things they may feel a little jealousy, but are able to tolerate it without incident.
Other women may be more insecure, and therefore will have little, or no, tolerance for such behaviors. For these women, if they catch you in such actions, it can cause big problems. It will make them feel as if you are not satisfied with them, and therefore that you may be on the lookout for something better and leave them.
