It's true that a partner in love can make one happy, no doubt. That love can be liberating, deep and precious. The downside, is that, this happiness is not permanent or lasting. It will disappear again and one will experience suffering as a result.
If one is satisfied with that, then no problem. One is of course free to do as one wants. Buddhism does not prohibit that. There are no judges or absolute commandments in Buddhism. One reaps as one sows. One is the sole inheritor of ones actions.
What Buddhism teaches, is that if one would like to achieve a permanent happiness then one should not look for it in conditioned existence (samsara), because it cannot be found in a world that is impermanent.
To achieve lasting and permanent happiness one must realize Nibbana, the unconditioned, unborn and uncaused state.
Nibbana is not subject to incessant arising and falling away, thus it is stable, secure and permanent.