Hello Eishhatorah and welcome aboard!
As you can tell by now you are far from alone here. I am in my 40s, married with kids, and I too have been dealing with SSA since my early teens. I never acted out with another person, but I fantasized and m*** incessantly and later on got hooked on internet g** p*** as well. I never even entertained the thought that it would be possible to stop until about a year ago when Hashem led me to this wonderful site and I discovered that I was not alone, and that it was indeed possible to cope with this Nisayon and live a Torah-true life.
I totally identify with your struggle in Yeshiva, i remember those days well. To have held back for 7 months...I barely ever managed a week or 2.
As for marriage, i can confirm what the "other" Eish said, marriage alone will not make it go away. You are lucky to begin to work on it now while you are single. I would also recommend that you look into JONAH, it's not for everyone and it's not a guaranteed cure, but it could definitely help. I just finished reading Arthur's book "Light in the Closet" and I found so much there that resonated with my childhood experiences and with my personality, and just understanding how these elements play into the development of SSA has really helped me cope with it.
Stick around and keep posting, isolation and loneliness is our worst enemy. And Keep on Trucking!
Gevura!
P.S. if you are interested you can find my whole story here:
http://www.guardyoureyes.org/forum/index.php?topic=4125.0