How to end this for good?

4 months ago, I was in relationship, my ex boyfriend a very good guy at the beginning, but after we went to different colleges in different cities, it became hard and I must admit, I fell out of love with him, so suddenly, I don't even love or like someone in my college, but he suddenly changed to everything I hate, and became extra selfish, so I just did, but I couldn't break up, instead, he did.
Originally my family opposed this relationship, they hated him, so he said he can't stay with me for 7 years, so my parents could come at the end of it and refuse to make me marry him. and so we called it off, but he said he would come few years later, and ask for their permission to marry me.

so I was fine, thinking it was over, but I became bestfriend with one of his own friends who entered college with me, and few weeks ago, (M) - Our mutual friend - came to me and said that my ex still loves me, and I shouldn't be so free with guys like this - although I don't do anything, I don't go on dates, I just have some guy friends, who my ex knew I had them -
I was pissed, I wanted this to be over, and then I found out my ex blocked me on facebook, but because (M) interfered, he unblocked me.
then I found out he blocked me again.
I want to end this with (M), I don't want him to mention anything again about him, I don't want to lie and say I love someone when I'm not, I'm not being cruel but being honest, if I said I loved him, then I'd be lying, but also I don't want to lose (M) he is one of my bestfriends now, so how should I deal with this if he talks about my ex again? how should I deal with it?

Please all of you help me
How to end this for good?
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