most of my relationships have ended smoothly. i've had one when i just kinda stopped answering her phone calls for 3 months then answered one and fucked her and then never talked to her again. but as for the rest i kinda just said 'listen this is what's going on in my life, when this time comes im probably not going to want to have a girlfriend'. its nice you end on good terms.
that's jsut me though, i must have some peace power with women. i've never even gotten into a fight with a g/f.