There can be multiple reasons for losing interest in sex by either party. It could be hormonal but sometimes it is due to trauma earlier in life. Dealing with that can require a therapist.

But another reason sex can be turned off is because there may be a sense of no sensitivity on the part of the partner to their needs. A woman needs 1/2 to 1 hour to be fully aroused. Men can be ready in minutes. Without that time of hugging, caressing and eventually foreplay for a considerable length of time, a women can be left just getting aroused by the time a man climaxes. Having an afternoon with no interruptions or distractions just being close and caring and responsive to the other's needs can make a big difference.

If the man postpones orgasm by shallow thrusts and resting when getting excited, with both partners laying on their side, joining can be an extended activity that allows the woman time for full participation. The Tao of Love and Sex goes into very fine details on how this can be accomplished. It is a 3000 year old text but has relevant techniques and ideas of sexuality for a society with limited ideas on what intimacy is. Was available on Amazon.