There is nothing to do with being pervert or anything. It's just that be ashamed to do a kiss with your lover is something that we expect from a middle schooler (or even a high schooler). Not from a 30-years old couple which are not otaku.
If all the point was about be ashamed of doing sex, ok, alright it would be fine for me.
But there is no sense to be ashamed so hard for a kiss (and, once again, they are socially fine).