Perhaps they had nothing else together. For a relationship to last it must exist on many levels. It is important to enjoy your mate as a companion with shared interests. Someone to treat as a friend and enjoy being with, no matter what you do. One level is romance and commitment.
Romance needs attention along the entire way.
Then comes commitment. You commit to yourself, your mate, and your relationship. It is wisest to select and nurture your relationship on all levels. Each level compliments the others. Be aware that on each level there may be history.