how to deal with this?

It all depends on how much you love your boyfriend. If you are really serious with him, definitely you will say no to that person & tell your boyfriend about this.
If you are not that serious & its just a relation, then its upto you to decide how that person is & whether you like him or not. If you like him, say yes, other wise keep it pending or say no.
Well this happened with me as I liked the girlfriend of my friend & I proposed her. Now she accepted it & dumped her bf
After all its survival for the fittest

oh, It is really happen to you? you must be a beautiful and kindly girl since you considered so much for that boy.But I think if you dont love him, you have the right to say NO.Just be yourself.Good luck to you!

smile and do nothing. ignore everything, unless you want something to happen - or not.

i think i will refuse him directly,and i will not tell it to my boyfriend.but if he still pester me after i refuse him,i will think about telling this problem to my boyfriend.we should face this problem together.But i think the premise of all is that i have enough charisma to attract two men.