Sex is definitely ok with a yogurt lubricant. In fact, it may help your partner defeat any low grade infection he is suffering. Don't use anything with Sugar or flavoring -- only PLAIN. This is also wonderful for your face, neck and body. It softens the skin as well.
The best is homemade yogurt, cultured 24 hours till it is very sour. That means less milk Sugar and more good bacteria. It is easy to make.
Scald 1 Qt milk & let cool to baby bottle temperature -- drops on the inside wrist aren't burning or cold. Stir 1 TBS live culture yogurt into the milk. Cover with a clean dish towel and put it in a warm (90-100 degrees) place for 24 hours. A good way is to preheat the oven for a few min and leave the light on after putting in the milk mixture to keep it warm. Don't open the oven or disturb it during this time. Remove it from the warm place, cover and refrigerate. It will solidify when cold.