I'm going to go out on a limb here and say that part of the problem here is that you have NO respect for, or interest in something that is a BIG part of your H's life. These games he plays are something that he clearly values and wants to pass the enjoyment of onto his son. I know I played some of those games when I was a kid and I didn't suffer for it at all. I still play video games and such, but I outgrew the other stuff. Just because your S5 plays the games now does NOT mean he'll play them all his life anymore than a son that plays baseball with his father will play baseball all his life. I know I am making a big issue of this but it seems like it may be a larger problem than you realize between you and your H. With me and my W the issue is video games. I play them and I let my S5 play them with me/by himself. If it were up to her, he would never play at all. She sees NO value in them and basically thinks that they're a waste of time. I'm sure, like your thoughts on your H's gaming, she also harbors the opinion that playing too many video games will lead to doing poorly in school and being a general "loser" in life. Of course I know MANY very successful people that play as much or more than I do (actually I hardly play anymore) and see no real correlation between success or lack thereof and video games. She's warmed up over the years and now even bought him a gameboy for his birthday last year and understands that while there are better things to do with a kid's time, it's also not the end of the world if he plays video games too. Last thing on this subject. You also said that your real problem was that they played too late, etc, and if it were during the day you'd have no problem with it. I think that is a bit untrue. I think you wish your S5 did not have ANY exposure to this game and it is causing you to react the way you are. YOU ARE NOT WRONG about this by the way, and I am not saying you are, I am just continuing to point out that your H's perspective on all this is VERY different from yours.
Sorry to go off on that tangent, but like NYS said, you are projecting the future here, and it may never come true.
As for your jealousy, part of that may just be the father/son relationship dynamic where at the age your son is now, he is just starting to identify with dad and take interest in his interests. Your role in his life right now is a little more undefined but no less important. I know in my family this is happening.
Finally, I just keep reading your posts and you keep going back to the issue of "well, we had an agreement" and the like. Yes, you did but sometimes there are battles that are just not worth fighting. This seems to be one. I really like what NYS said about totally letting go of the situation and making your H handle it. He IS an equal partner in all this and if he thinks there is a better way than the way you two have discussed, then fine, let him have his day (or week or whatever) in the sun. Will it irreparably harm your son? Let your H take care of all the nasty bed time, rule setting stuff and you just kick back and try to find new ways to have fun and connect with S5. When your H starts complaining about the burden, or your lack of help, don't rebuke him, kindly offer suggestions, if you have any, that may assist him and go back to what you were doing. If he gets more forceful about things, then kindly remind him that you would love to help more but don't want to make him think you're trying to get your way or be right. Do NOT be snotty or "I told ya so" about any of this. Again, it's about HIM asserting his parenting...er...skills and not anyone being right. The goal of this would NOT be to watch him fail. The goal would be to actually have him succeed, and have it be something that YOU backed off and allowed him the space to do. You may question if he CAN succeed, but it will be much easier for you to accept his input IF he does succeed, and much more likely that he accept YOURS if he fails. It's a win-win, no? I understand your fears, but also understand that if your marriage fails and you S or D, then your H will be totally free to play games with S5 as late as he wants and you will have NO real say in it. It seems better to let go a bit and see what happens. Just my 2.5 cents.