She is not your sister, cousin, or even distant relative and she's somebody's wife and you are a man but you are busy texting her "dear umeamkaje, dear umekula, dear take care, dear have a good night, dear God is good...", ...
He is not your husband, brother or even distant uncle, you are a woman and he's somebody's husband and you are busy texting him "dear umekula, dear umefika salama, dear usiku mwema, dear ninashida ya hela kidogo..."
You are a friend, its ok but you are not responsible for his or her emotional satisfaction, that's his or her partner's responsibility. Stop being in between two people, cut the emotional string with somebody else's spouse. You can be friends but do not confuse your place with that of his wife or her husband.