I find it interesting that poeple didn't seem to read your entire post. You say you are not considering moving in for another 6 months and are thinking things out in advance. This is good. While I agree that when kids are concerned it is best to wait until you are married until you move in together, that is not my call.
(oops! accidentally posted without finishing!)
Anyway, whether or not you are thinking of moving in another person into the house, it is time for the boys to learn to sleep in their own room without you. You say they would be staying in the same room and you and your boyfriend would be taking another one? If that is the case then the transition will be much easier since the location the boys will be sleeping in will not change, just the company. :o) Do you put them down by themselves at this point, and then go to bed yourself at a later time? If not, try that first. This will get them used to falling asleep without you in the room. Next, put a blow-up matress or something in the room that will become yours and just sleep on it one night and see how that goes. They may not even notice! If they wake up in the night and notice that you are gone, just go in to them and assure them you are right in the other room and can hear them if they need something. Then tuck them back up and go out. After a couple of weeks of this, tell them that you miss your bed and are going to move it into your room. Just make sure you do all of this now, so they don't associate the sleeping change with the new man in the house. You don't want them to think he took you away from them. Besides they are plenty old enough to sleep in their own room regardless of what may be happening in 6 months time.
Again, I do think it is best to wait until you and your boyfriend have committed to a forever relationship by getting married before you make him a 24/7 part of your kids' lives. That will make them feel far more secure and help them to commit to a healthy and loving relationship with their new step-dad, and not keep themselves guarded and closed off just in case mama's boyfriend leaves one day. I know it is not popular now and some people think that marriage is just a piece of paper, but that piece of paper equals peace of mind. It makes couples think twice about splitting up just because things have hit a rough patch. That is my opinion and please do not think I am judging you. You have the right to make your own choices and seeing you ask these questions so far in advance tells me you plenty smart and a good mom. It is just my experience with life that compells me to share this advice. :o)