No judgment on your addiction. It doesn't matter what anyone thinks, you acknowledge it is negatively affecting your life and impairing your ability to accomplish your goals.

It's really a two part problem, your addiction and your school.

For the first problem, have you gotten any help, therapy or support groups? My town has a sex and love addiction anonymous organization. It works like AA with a different focus. They would be a resource to find a therapist who deals with sex addiction in a frank, non-judgmental way. My therapist does quite a bit of counseling for sexual issues including addiction. In the limited number of sessions I have discussed sex. I found her to be just that, frank and not judgmental.

Ok part two, the school issue... It is going to take switching your focus from addiction to studying. I have a lot of trouble focusing myself. I can procrastinate way too much. I tell myself the assignment isn't that big and I can do it in an afternoon. Cut to midnight it's due at 12:01. I am tired and still working on the assignment.
My best advice for this is to be incredibly honest with yourself. I know working on a research paper I will get bored, a lot. So I try and figure out. I will take x number of breaks, I will probably get distracted by Facebook for about x number of times.
But be realistic. Then work with those realistic estimations. For instance, I am bored researching widget production so I take a break knowing I can and I have two more left. I may even set an alarm, when it dings break is over, back to work.

I hope this helps.