First, let me say that all relationships have their ups and downs, and sometimes you are sailing along full steam and then you hit the doldrums.. it can and does happen. But, there are things you can do! Love isn't a feeling, it's an action, it's a choice we make every day..
In the early part of my marriage, we didn't really know how to communicate well - we'd have a problem that just seemed to hard to talk about, and so we would let it slide - and that just led to lots of resentment and sorrow. Now, we have learned to have those really awful conversations with each other realizing that we aren't fighting with each other, but having the conversations like we are on the same team (which we are!).. so, just like a team, you talk about what is working and come up with some strategies etc.. Let's say your husband is doing something that really bothers you, you have to tell him.. not to correct him, but so that the situation can be resolved and you can go on feeling good about the relationship. Almost all problems can be fixed with good communication. Find it too hard to talk about something? Write him a note - this can be very effective! If you go this route, though, be very careful, because it is in print, and you can't take it back - make sure not to be accusatory, but talk about more how you feel. So, just as an example, (just picking something random here) let's say your husband watches porn and you can't stand that.. in your letter, just say that it makes you feel bad about yourself etc. and that you wish he'd stop, so that you could feel good in the relationship again.. always say (and write) everything from a place of love and respect - the last thing you want to do is hurt him, which will only make it worse. In the end, find a way to say what you gotta say.. this is the beginning of fixing things.
Secondly, just start acting like he is the love of your life, again.. studies show that when we are happy, we smile, but it also works the other way - smile and you feel happier - this is honestly true. Same with small acts of love - we love the people we take care of and acting loving towards.... put little notes around the house for him, buy him a present, take him on a picnic - do for him, all the little things you would like for him to do for you - plan a trip, go for walks in the park etc.. It may not be your fault you are in a rut, but you are a team - be the one that pulls you both out of the rut!
Lastly, I just want to say, think about the alternative to having him in your life.. I know some divorced people who thought that life would be great once they were separated, only to find that they now have a whole new set of problems - loneliness, other relatives that are hurt by the separation, that feeling always hanging over your head "did I do the right thing? Could we have made it work? - quitting is never going to be a good answer - hang in there and fix it..