Every relationship is composed of at least two people and both of those people have feelings they bring to the relationship. Half of those relationships belong the guy in the relationship. Despite traditional definition of masculinity, men feel just as many feelings as women do and they feel them throughout the course of any and every relationship. This done not mean that each guy process the emotions the same way or even understand them the same way. Guys can be fluid about their feelings as they pertain to friends with benefits relationships.
Some guys are just like the stereotype. They will take what they get and will often use female friendship as a means to get women to hookup with him. These guys may completely stop speaking with a girl after the conclusion of the hookups. And they may be able to transition the relationship in and out of friendship without thinking twice about it or how it may affect the people in the friend group or the girl within the friend group or the girl's relationship with him.
Some individuals are selfish and focus solely on what feels good for them with the rest of the group not getting a moment's thought.
Some guys are a little more in touch with their feelings than others. They may care about whether or not they are leading you on. They may care about how this will affect the friendship group. These are the guys who care out of a genuine place about how the relationship will affect you and his friendship and everything outside of the group.
These guys will have continuous conversations with you to ensure that you are okay with what is happening and how you feel about the casual hookup throughout the process. This guy will do everything he can to continue the friendship and not affect the group beyond what the two of you are doing. He'll want to keep you a part of the friend group even after the relationship dissipates.
These are the guys who are using the casual hookup as a way to get a relationship. These are the guys who may have started this hookup assuring the girl that this is casual and they are cool with it and there's nothing real behind it, but these guys exist and they exist to ruin friends with benefits relationships. They are convinced that they are the guy this is going to work for despite all of the evidence to the contrary.
These guys shouldn't be looking for casual friends with benefits relationships but they continue to do so because they may not have other options. They may have brought a crush into the friend group to better know them and establish a casual relationship as a means of transitioning to something real. These relationships will never end well for either party and may end up costing the girl the new friends she has made.