How to unfriend someone politely without them knowing it's intentionally? ?

Be busy. All the time. If he calls, tell him you are with friends and you will talk to him later,  And hang up.  Just keep doing that. Just be unavailable. This does eventually work. I’ve had to do this on a few occasions. Some people just can’t take a himt

There is nothing better than plain old honesty.  That way you have said what you have on your mind, you will not have to keep pretending or running or ignoring.  So what if he gets hurt.. he will be hurt more if you play the game of ignoring.  

Trust me.. I have played those games before in my younger years and karma got me.  So. in my old age, I have learned to be tactfully brutally honest and it has gain me more self respect than the old me ever had.

Tell him all about the great sex you're having with your boyfriend.  Make sure you emphasize that you'll do ANYTHING for your boyfriend, anytime, anywhere, and that you LOOOVE your boyfriend SOOO much, you can't wait to get married.

Eventually there will be crickets.

Just tell him you're not interested in him.

No matter what or how you do it, he will be hurt anyways.  Just do it and move on.

Some people just can't take a hint. You have to belt them over the head with it, until the message gets through !  But I think your best bet is to be totally unresponsive, if you have already made it plain and clear that you aren't interested in continuing a friendship or any other kind of relationship. If you are delicate and subtle, it may just completely pass the ignoramus by.  But once you've made your wishes clear, then stop responding , entirely. that will end things soon enough.   

Just take longer to reply to him and try to seem as uninterested as u feel hell probably get it