Saying 'No' Nicely

[blueyedbrit]

My boyfriend's roommate, lets call him Jake, wants his girlfriend, lets call her Jen, to move in with them, but my boyfriend doesn't want to live with them. Jake is trying to convince my boyfriend why Jen should live with them, and says he's even thinking about proposing to Jen within the year. My boyfriend thinks Jen is annoying, plus who wants to live with a couple on the verge of getting engaged/married? Isn't that weird. My boyfriend has already said no once, but Jake has asked again, in a sort of "final plea" type of way. My boyfriend and Jake have been friends for a long time, so he doesn't want to hurt the friendship. How can he say no nicely?