I keep no secrets from my SO. I hope she keeps none from me.
I will never ever NEVER break her heart. That means no cheating of any kind or form or Bill Clinton definition.
My SO knows everything about my CDing. It was NOT easy for her and it was even worse for me while she came to grips with it. An I told her BEFORE I started. Once she began to believe me and not add anything to it, she became happy again.
Stop the "boyfriend" because it is going to bite you one day. Think this through and decide if the thrill is worth the risk. It isn't. You have NO IDEA how your SO will react. Remember "Hell hath no fury as a woman scorned". That old saying was based on fact. You read on this forum of SOs having fury just finding out their guys are CDers. Throw CDer in with having a fling AND a fling WITH A GUY and believe me you will get a good glimpse of hell.
Think about all of this with the head on your shoulders.