your DH that SO MANY 'kids" who reach adulthood (in years anyway)  refuse to launch. You guys are so fortunate!

As for him having an issue with your oldest, I'm not sure if this is your situation, but I was single for a long time and it was just me and my kids. My oldest son was very protective, and almost seemed to take on the role of "the man of the house" and anyone (there were very few as I worked and attended college all the time) I had a date with was really under the microscope with him. Perhaps your oldest son is like that, I don't pretend to know, however, I am sharing my experience. If that is the case, your DH may be picking up on it and that may be what' s making him uneasy.

Were there any issues with these 2 when you were dating your DH for 3 years?

I don't know how to make it less hurtful, but if your DH is open to discussing it, maybe that would help.

Be proud that you've raised kids who are "adulting." Never let anyone make you feel anything buy pride for that. You did well in raising your kids.

Can you push further when you two do discuss it? I've had situations like this with various relationships over the years and although it's difficult to prove, it usually turns out that our "intuition" is correct. Can you use his actions to help him see things from your point of view? For example, if he makes a comment about your son and you sense a hidden message, ask him how he'd feel if you said the same thing about his son. 

Since there are other kids involved and you're only sensing this with one of them, I'm guessing there is something going on for your DH in terms of your older son. If it's jealousy, jealousy for what? That his son isn't as successful? Jealous that they aren't as close as you and your son? If you had to guess... what do you think the problem is?

As for making it less hurtful, I agree with MissTexas - you've done a great job of raising kids who are succesfully adulting - try to remind yourself of that. If your son hasn't done anything to deserve your DH's feelings towards him, it's DH's issue, not yours. And definitely not your sons. 

That's kind of vague, what do you mean he's "jealous of your son's success."? Could it be that your son treats him poorly, or is arrogant, or something about your son's behavior that makes your DH dislike him?  Unless your son is a millionaire by 27, I can't picture a scenario in which a middle-aged man is jealous of a young adult.

^^^THIS^^^^

I cant see a grown man, your husband, being jealous of your adult bio either. Thats weird.

I would highlight the individual acts that your husband does that feel like they are done from a jealous place. Don't accuse your husband of being jealous, you don't know what his emotions are and that will just rile him up.

But do ask him with an air of innocent curiosity "why would do you say that?" "why did you do that?" type questions to force him to articulate why he treats your kid's differently so that hopefully he realizes that it is not justifiable and will stop doing it, (at least in front of you anyway). 

... at least in my experience. If I'm being honest, I have to admit that part of my distaste for SS28 is that he has achieved a basic level of success in his chosen field, whereas all 3 of my offspring , while fundamentaly sweet-natured, are ne'er-do-wells of various flavors. However, it's pretty clear to me that SS, besides being a nasty piece of work, is heading for a fall. My kids are at least nice (mostly) and ... well, let's just say they don't have far to fall.

Oh it happens. My exH was extremely jealous of one his bioS, our son together. ExH was always trying to one up BS as a teen. As an adult BS has surpassed him in every way, which is what we want our kids to do right?  I always thought this dynamic was weird. 

Call DH on it.  Lather, rinse, repeat until DH catches a clue.

It definitely happens. Some of my ex's adult kids have kids they won't work enough to support, so they call him regularly for money or just don't take care of their kids. My adult kids are childless and independent but he had the nerves to say when they have kids they might not work and take care of them, and that they could already have kids I don't know about because they aren't taking care of them. I was like WTF?? Told him don't wish bad things on my adult kids just because his are troubled.

After we were together for awhile, he found out my kids and I used to travel quite a bit when they were under age and that we have taken trips together since they have become adults. He even realized they travel together. Next thing I know, he wanted our trips to include his adult kids and told me to invite my adult kids. That  is until he found out I wasn't helping fund the trip. My adult kids could afford it. His couldn't. Needless to say the trip didn't happen. He said people who have jobs and are able to take care of themselves are just "lucky." As if no hard work, dedication, or desire to be independent goes into it. Smh