I think it would be best for you to NOT remain friends with him, because its clearly not helping you get over him. Why are you texting/ringing him? Isn't it hard enough already, that your making it even more harder by trying to hear from him and know what he's upto etc? Seriously, keep a distance. Make new friends, find activities to keep you busy.. focus on yourself only. Also, build on your self-respect.. being clingy by texting him and whatnot isn't showing any respect to yourself & your feelings.
Hope things get better
