I'm thinking here of DPs who've become inattentive or flaky, or are taking you and the relationship for granted, rather than the vile abusers or those who've acquired an OW.
Wondering what's worked for you to bring them into line and make them realise that they need to stop being useless put more into the relationship or you'll be off in theory, anyway.
These have, to some extent, worked for me in the past:
Told him I was being considered for a purely ficticious promotion but I'd have to spend every third week in London with that drop dead gorgeous boring guy from head office 
Over a period of a week went from looking like a bag lady to being fit to be seen in daylight transformed my appearance.
Let him take the lead with texts/phone calls/meetings - only responded when he made the first move - found this one really difficult due to being needy and a control freak
When we did meet, was very light and bubbly probably seemed a bit mad, actually with no talk of us/the relationships/problems/the future.
What have you tried? And what's worked?