Every girl says she wants a nice guy. But, then she leaves the nice guy in the black hole of the friend-zone and starts dating the most not-nice guy. The nice guy is devastated. He thinks he is the one that clearly belongs with the girl. After everything he did for her, he deserves her. Well, if this is the type of mentality that the nice guy has, he probably is not a nice guy.
If men form friendships for the sole purpose of prospective romantic relationships or with the goal of sexual favors in mind, they are not nice guys.
If men feel they deserve the romantic affections of their female friends because of the effort they put into a relationship, they are not nice guys.
First, that is what friendships are about. Each person puts in effort to maintain a good relationship. Second, women do not owe men anything. This includes their romantic affections, sexual favors, or their bodies.
Are there some women who may take advantage of their male friends? Of course, and men can take advantage of their female friends too. Perhaps they are aware of the romantic affections of their male friend and ask him for various favors at ridiculous hours. She still does not owe you her body or her affections.
Also, if you feel you are being untreated fairly by your friend, maybe tell them instead of expecting them to be aware of your feelings. And if your friends still disrespect you, maybe it's time to find new friends.
Are there any truly nice guys? Sure. But, in the context of heterosexual nice guys who finish last or nice guys who claim to be in the friend-zone, probably not. Nice guys may be nice to the person they like and horrible to others (just like a lot of people). In my experience, nice guys are nice until they're not. They are only nice until they don't get what they want.