So sorry for your loss of your husband of 17 years, but it sounds like you've coped and are ready to move on and live life... I agree that it's healthy to be happy and find what makes you fulfilled, although I don't agree with pushing your children away over any man. This man may be wonderful, but he needs to support your love for your boys and respect your decisions. You still have a dependent especially if he has ADHD. I don't think this is the time in your life to be leaving him and taking a trip with a man you don't know all that well, especially if your son from overseas may be coming home during that time. Your boyfriend should respect/understand that. This could be the beginning of how he treats your boys if he feels comfortable leaving your youngest, and not being present for your oldest. You'd feel terrible if you missed your son while he was home from being overseas, and something could happen to him when he heads back and you weren't around to see him when he was here.
My parents are in the same phase right now as you seem to be, and a lot of their behaviors are selfish, but they don't realize it because they don't want to be held back. They had us kids when they were young and now they are 52 and 51 years old with all grown children (29,27 & 24). I don't have a problem with many of their decisions, but for example for Christmas I'm having Christmas here at my house with my brother and his family and my parents were going to go up to their cabin 9 hours north????? Doesn't make sense, but after talking with the both of them they realized that it didn't make sense that they would want to go by themselves to their cabin instead of spend Christmas with their 5 grandkids.
I think your oldest son is very sensitive and mature. Appreciate that he does care so much about his mom. Show him your appreciation and the communication will get better, and support will follow. You need to think like a mom because that's all your 25 year old knows you as.
Anyways, good luck with that one. Enjoy your family and good luck with your new relationship.
Overtime, with your son knowing your love and support for him he will accept you dating and eventually support it if your decisions are rational and loving...
Hope I helped, I don't mean to be rude, I can be pretty straight-foward and my mom sometimes doesn't like what I may say....
L.