hiya,
everyone is different.some men look at other women and some men don`t. do you love this man? if you do then you need to tell him how painful you are finding his actions. if he loves you he will stop. i am 29 years old with two long term relationships under my belt and i don`t know much about how to keep a relationship going. but i do know what will kill one stone dead,-lack of communication. you must talk to him, if you don`t it is over.
the issue of trust will resolve itself if you talk to each other openly and fully. i wish you the best of luck