No easy answers here. You know him far, far better than any of us ever will.
No, being a bit bored in the bedroom and curious isn't a wrong reason to want to swing per se. If there's problems in the marriage, for example in the bedroom, then swinging won't fix them; it'll just make it worse.
The #1 best thing you can do is love him as deeply as you do. Also, don't play games with him. That said, you can skirt around the subject over time, planting seeds as it were, and maybe eventually he'll start to wonder what it would be like. Another thing you can try is having a very open, very honest, discussion between each other. But, make it crystal clear that it is a discussion ONLY and there is nothing in any of this that means you love him any less.
My wife was absolutely 100 percent against the idea of swinging. There was no chance it was ever going to happen. I'd dabbled in the lifestyle before meeting her, just with one couple, and she was not happy about it. She wasn't judgmental per se, just that she knew there's no way she was ever going to do that. Fast forward a few years, and we're considering getting a Sybian. A local swing club has one, as I found out, and I suggested the idea of going there to try it out. Bzzt; wrong answer. Not going to happen, no way, no how. That was ~4 years ago or so.
Now, through all of this I never engaged in any conscious effort to get her thinking about swinging, or to even consider it in any respect. I was absolutely content that we'd never swing. No worries, on with life with my wonderful wife. And then...
About 2 1/2 years ago, she brought up a scenario of very, very light swinging; just having a few men give her sensuous massage, with her naked. Fast forward to now, and she's had sex with many men in the lifestyle, some of them multiple times, and thoroughly enjoys the lifestyle. She's very glad she's a swinger, and looks forward to swing encounters.
You just never know.
Time, patience, love, honesty, communication, togetherness. Even if that doesn't pan out in the two of you swinging, it's still 100 percent worthwhile.