Complex sentence: When Sean became jealous of Marcus staying with an ex in London it became clear that it was time to move on from Marcus; on 3 September 2008, at a party at Liam's, Sean fell for Tom Kerrigan.
Split into simpler sentences: When Sean became jealous of Marcus staying with an ex in London. It became clear that it was time to move on from Marcus; on 3 September 2008, at a party at Liam's, Sean fell for Tom Kerrigan.