why is the narrator annoyed at the behaviour of lovers in general ?

Jerome does not like their public displays of affection when he had to share the same space as them.

You walk down the path, and as you pass the summer-house you glance in, and there are those two young idiots, huddled up into one corner of it; and they see you, and are evidently under the idea that, for some wicked purpose of your own, you are following them about. “Why don’t they have a special room for this sort of thing, and make people keep to it?” you mutter; and you rush back to the hall and get your umbrella and go out. ch12