>>213642812He didn't "do" anything, thats entirely the problem, he chose the middle ground in every opportunity of the relationship rather than just saying no when she found the ring or actually giving the relationship his full commitment.
Instead he actively spent every waking moment avoiding her by gyming or trying to cheat or not engaging with her because he wanted to simply have the respect that a normal married person would get while being a complete coward by not investing any of his time into it.
S4 is amazing and i wouldn't change it but if you watch that season and think Mark isn't the worse person (which is saying a lot because sophie is a shit), i don't know what to say