Many great relationships began with one person becoming attracted to another.
In some other instances, both partners just become drawn to each other instantaneously, and without much effort.
While many things are needed to keep that relationship going, the attraction which ignited the relationship remains a very major key, and once it starts to wane, all the other good things in that relationship might no longer count for nothing.
Tell them about it
It’s not a bad idea to tell them. In fact, it’s pretty necessary, since all great relationships are based on open, honest communications.
However, to achieve the best result, think about the best way to start your conversation so as to not upset them.
Remember, this is delicate.
Never let them think it’s their fault
It is not advisable to approach the matter in a manner that is too critical or one that will leave them downcast and unhappy.
Let them know they are a wonderful human being. And it is really at this point that it makes sense most to tell them that you really love them so much.
Reach a compromise
During the conversation mentioned in  above, take time to mention the things about them that you were so attracted to, or things about them you no longer find appealing.
Suggest the type of changes you think they should make. Just try to not be so insistent or sound too critical.
Whatever their final decision is, let it be because they see reason why they should do it, and not necessarily because you threatened to leave them if they did not.
Of course, they’ll be willing to make little changes to recreate the spark in the relationship if they really care about what you both have.