I think you should suck it up and let your partner do his thing. ... "This makes me uncomfortable" isn't always a cue for other people to modify their behavior, no matter the mores of our times.
And in fact, you're already perceiving the situation as such. You say their kissing "obviously" isn't sexual, and that you are pretty sure that this is a you problem. When you think the problem is you, it's up to you to fix it. Leave these people to their affection, which is a nice thing that exists in a cruel world.
[
add
]
[
|
|
...
]