Hi be_be
A couple of things come to my mind as I'm reading your post. First off, it doesn't sound like either one of you have much invested in this relationship aside from the sex. If you are going to be friends with benefits, I can tell you that sooner or later, feelings are going to be hurt. One is going to feel more than the other. When that happens, it changes the whole scope of the relationship and no one ends up being happy.
The next thing I think of is that if either one of you has sex with another individual...even if you tell, and you have unprotected sex...then you are sleeping with whoever they slept with. The chances for spreading/being infected with something is extremely high.
The next thought is pregnancy. The only absolute to not get pregnant is abstinence. Are either one of you prepared to raise an unplanned for child?
My thought is that if you are questioning this situation, then you must not be feeling all warm and fuzzy about it to begin with. If that is certainly the case, then please think long and hard about the ramifications of what you are both doing. I can only see a lot of hurt and possible illness coming from this kind of an arrangement.
Please take good care of YOU. YOU deserve it!

sabby