If you have wandering eyes, the mind wanders and then next the body. It is completely disrespectful to your partner to wander in any way or form. If you want to lust after other people, then do your partner a favor and leave. In my book, looking at other women, men (whatever the case may be) is the same as cheating (wandering eyes, wandering mind). If your partner isn't enough, then leave and go play the field. Not all men are like that though. Some men are completely devoted to their partners and are completely satisfied in their relationships thus having no need, lust or want to stray in any way or form.
I'm sorry....it just really bothers me that this is considered normal. However, your stepfather's bahviour is very far from normal.
It sounds like your stepfather needs some serious help...professional help. There are docs who specialize in this sort of thing. It's a sort of sex addiction. You and your mother need to do an intervention. Maybe family/group therapy as well, as his behaviour is now effecting you and embarassingly, the community. Give him that chance to do something about it, and then if it continues....your mother needs to seriously rethink her marriage to him.
I'm sure your mother deserves to be treated like the tolerant and loving wife she is.
Good luck to you all.