You can get divorced by relying on your spouse’s unreasonable behaviour. The test is a subjective one and not an objective one, which means that when the district judge reads your petition (s)he merely has to be satisfied that you find the behaviour unreasonable. It is not a ‘man on the Clapham omnibus’ test.
This does not mean that you can rely on trivial grumbles about your spouse. Remember that the district judge is trying to decide whether the marriage has broken down irretrievably. Generally, the more serious the behaviour you are alleging the less you have to put in your petition. The shortest ‘particulars of unreasonable behaviour’ I ever drafted was for a wife whose husband told her after the wedding that he had changed his mind and that despite what he had always said he didn’t want children after all. A single sentence explaining that was enough to get my client her divorce. She had to wait, though, as you’re not allowed to petition for divorce until you’ve been married for twelve months.