Most Helpful Guy
you do not ask, you demand it. If you want a monogamous relationship, you have two options, marry him, or insist that, if you are going to to have sex with him, he must be ready to be only with you. This usually takes time in a relationship. Most men, if they are not married (and even if they are sometimes), believe that they have the right to play around until they marry someone. So, you need to know what kind of guy heis and if he is interested enough in you to make it a monogamous thing. You have to tell him that is the only way it will work. Still, you will need to know him well enough to trust he will live with those terms, not just agree to them.
Most Helpful Girl
I make sure the atmosphere is playful and then say, "You know what? I really like you." and then hear what he has to say and then I'll say, "So what do you think about me?" and then usually from there, you will know what he looking forward to with you.