If you and your significant other are having problems getting along with one another, you need to go back to the fundamentals that every relationship should be built off of to work. These include trust, forgiveness, and the desire to make each other happy. If your relationship is missing any of the 3, then maybe its time to move on.
Trust is the first thing I list because if you don't trust your significant other, then you can never truly be comfortable with them. What kind of a relationship is it if you have to worry and fret that they'll do something, anytime they (or you) walk out the door? You need to find a way to trust your significant other, and if they can't be trusted then you have some serious issues to workout, or your relationship is doomed. A few great ways to build trust are to go on small outings without one another, and check-in with each other with a small text or a phone call explaining whats going on and where you are. It may seem overbearing at first, but once you are reassured with their location and actions, then you will soon be able to trust them. Remember, honesty is the best policy.
Forgiveness is another key thing to remember when dating (or anytime really). People make mistakes, its just a part of being human. Another fantastic part about being human is the ability to forgive. Forgiving one's mistakes will make your relationship stronger than ever. The old saying "Don't sweat the small stuff" really comes in handy in the dating field. Once one passes the "honeymoon stage" of a new relationship they will soon begin to notice small things that irritate them about their significant other. You have to find a way to overlook these things, are tactfully point them out to your significant other in a way that isn't hurtful, and offers a solution. Likewise, you must be able to take constructive criticism when it comes to your own annoying habits.
Putting their happiness before your own will very likely solve any problem that you have getting along with one another; but it has to be a mutual feeling. If you feel that you no longer want to make each other happy, then try to find your similarities or common ground; and if physical attraction is the only answer, I have some bad news for you. You need to be able to build your relationship off of more than physical attraction to be able to get along with one another and to keep the romance alive. Take interest in what your significant other is doing. Ask them about their day, ask them questions that can help you build an understanding of one of their interests. Simple things such as good morning texts, or surprise dates, or even little notes, tend to brighten everyone's day. Just some sort of small reminder that you are thinking of them.
Bring back these fundamentals and apply them in your every day interactions with each other. You'll find that you can rekindle that romance in no time, and go back to being the happy couple you started out as. As long as you remember those 3 things you can make your relationship last a lifetime.