Complex sentence: The next few weeks are extremely difficult for Nick so he is delighted when Leanne returns and wants to give their marriage another go, but struggles to cope with his tantrums and short tempers.
Split into simpler sentences: The next few weeks prove extremely difficult for Nick without Leanne, but he is delighted when she returns. Nick is over the moon when Leanne tells him that she wants to give their marriage another go, but she finds life extremely difficult with his tantrums and short tempers.