Communicate: talk about things, the good and the bad. Build trust. Be honest. Be faithful. Be there for one another. Make time for another. Leave the past to the past, which inculdes ex's.
Know that having arguments is normal. Know that you won't always be happy. Don't expect change. Appreciate the flaws. Appreciate each other. Become best friends. Lastly, love each other unconditionally.
Maintance a relationship is not easy because you needed to do all things that I said above and you must know there is must be always a gap but if you trying your best to maintance it and you really serious in your relationship.
I'm assure you that you will make it and you will achive your goals and I know is not gonna be easy, you know why i know?, because I've been on that situation before and now I've been in that situation again.
Which I also do the same trying to maintance my relationship with my partner but one thing that I must remind you in this journey it's need to be two side not only one side because if you both really want to achieved your goal and to maintance your relationship you both needed to try to maintance and walk together on this.
And I am always trying my best to make my partner happy and try to maintance oyur relationship and he do the same and so far we just doing alright but doesn't mean we didn't have argument or anything we do have it because it's normal but we try to fix it together and talk about until we find our solution for it, so the important one is in relationship I guess it's communication.
Don't be afraid to ask or start a conversation with your partner if you feel like you had something to talk about because if they really loves you and they want to walk together with you in this path they will try to listen to you and you both gonna decided and find a solution that's all is matters.