Yes Kaly, if you told me you are 'seeing someone', what you are really saying is; 'he is my boyfriend - and - You (that's me) will not be my boyfriend'.

Yes it does.

It means that you’re still dating several men, and you're still not in a committed relationship with any of those men.

Thank you Tom!

I´m not sure about other English speaking countries, but in British English there is a difference between saying ´I´m seeing someone´ and ´I have a boyfriend/girlfriend´, i.e. if you say you are seeing someone this indicates that the relationship is just beginning, e.g. you´ve been on a few dates maybe or talk a lot but you aren´t sure yet if you want to get more involved, whereas if you say he/she is my boyfriend/girlfriend, then you have already made some level of commitment.