Have you Talked to your BF about your BDSM thoughts? You never know, he might be sharing them.
As for knowing that you would not enjoy the act, How do you know? I would suggest that you explore that area of your desire and find out if you would enjoy the act or not.
What ever you do, don't just repress the urge, (which seems to be what you are trying to do now), for it will find a way out in an uncontrolled way, that could hurt you and others. I'm fully off the beleafe that half of what is wrong with the world is caused by some kind of Repression.
If you want to find a way to get the BDSM out of your system, without hurting your BF, then try going to a local BDSM club, and see what they have to offer. (telling your BF where and why you are going as well)
When I was in my early 20's, I was thinking along the same lines you are now, but after I went to the BDSM club a few times, and had a session or two being tied up and having my back worked on, I couldn't imagaine leaving the BDSM behind me forever.
Accept it as part of yourself, and don't let it control you
Just my 2 Cent's.
Wolfie