I am gonna go out on a limb here, and just give my gut feeling.
If BF is this way, and has been this way for 4 years..... well, if it looks like a duck, walks like a duck, quacks like a duck. I know that they are young, and may not be ready for marriage, house with a picket fence, and 2.5 children. But, he can't even get off his duff put away the video game to spend time with with the woman who loves him.
Yes, you have 'invested' four years in this relationship. However, any investor knows the old mantra that you simply do not throw good money after bad.
I know how hard it can be to create change, and consider ending a long term relationship. But, if I were the OP I would be doing some deep soul searching, and asking myself if I would be happy ten years from now, taking care of the house, kids, everything, and still spending 'lonely' weekends, cause my DH just 'isn't quite ready or motivated' enough to connect emotionally and to put his fair share into the marriage. Remember, some guys, like Peter Pan, just don't want to grow up, and are happy to live in never-never-land.
OP: You need to think about this and make your decision, regardless of 'hot guy'. You should make a decision to be in a relationship, based on that relationship, not the fact that there might always be a 'hot guy' somewhere out there. Don't ever let it be said that you were not commited or faithful, or that you let one guy come in and take you away from another.
Look into your heart and your gut. Make your decision to be happy with the status-quo, or to let BF know that you just cannot continue to stay committed.
It would not be mature, or wise, to go out with 'hot guy' and wait for a commitment from him to end your commitment with BF. And, it would not be mature or wise to use 'hot-guy' to try to manipulate BF into making a commitment that he is not ready to make, and might very likely not live up to. Either of those actions would only breed anger, resentment, hostility, etc...