I see sex as a process of mating which can be immensly pleasurable.  Sex is a process that lasts for sometime (10 -15 minutes to 45-60 minutes).

Love on the other hand, is much more deep and complicated thing. I would say that Love is also a process. But not shortlived as sex. The process of love lasts much much longer (at times one human life).

Is sex necessary for a healthy love life? Before answering this question, I would like to say that I personally think that love and sex can exist in isolation. That is to say that, there can be love without sex (Eg., love for our parents / siblings...We are anyways not talking about love for parents/siblings). And similarly there can be sex without love (Eg., Sex with a prost. / gigolo)

Coming to the question now. Views on this might vary, but  I think that though love and sex can exist in isolation, sex can act as a catalyst for the process of Love. It helps two souls to come closer.

To Conclude, sex is not necessary to lead a prosperous love life, but can help.