If someone isn't interested in you romantically but you are interested in them romantically, you have to end the friendship because it isn't good for either of you. This puts you in the position of being a creepy person pushing for romance with someone who has said they aren't interested and him in the position of taking advantage of your feelings. Both are bad looks and not fun for either of you. Also, you should have done this years ago when you got the first "not interested", so you're going to have to learn bad habits which will make this more difficult to do.

Don't distract yourself with other activities. Find fun activities that fulfill you more than an unhealthy one-way crush. Also, be very honest with yourself about how creepy and sad that was because that embarrassment and guilt should help you "get over him". If I was in your position, I'd be so overwhelmed with guilt and embarrassment for pushing myself on someone who was not interested for 3 years (3 years!) that I wouldn't ever want to be seen by him again. That would completely overwhelm any feelings of loss.