I also have a friend in RL who has gone through this, though she did start out loving her dp, but the years of all romance and effort (including making the effort not to be hungover or mashed on her birthday) coming just from her killed that love.
True, you can't expect teenage feelings anymore (though who would constantly want that up and down insecure feeling in everyday life where you need to be responsible to help dcs and hold down a job?), but you do need to feel you are valued.
The relationship ended recently after he found out she'd been having an affair with someone who 'got' her at last (I was very down on this, having been on the receiving end of one, but also because as a bystander I could see the new man was actually very unsuitable - still gets ex living down the road to do his washing though she was just blinded to this after being so romance starved for years).
Point is, her ex and friends and family now can't see it was all his fault, all they can see is the affair. Sad, because she tried to tell her dp many times about her unhappiness and even tried counselling but he didn't listen. When she started to get truly depressed by it she turned elsewhere. Now she shares parental custody with someone who hates her.
Feel free to use this tale in talks with him to drive home how serious the matter is, because it is a route you might end up going down. But if nothing can be saved, get out before you turn elsewhere. Otherwise, sadly, you will be forever labelled the bad guy.