Shouldn't my friend hang in there little longer?

My best friend have a perfect marriage.Her and her husband bee married for 10 yrs. Just 3 yrs ago they brought a nice big house in the country newly built.
She feels now because they have been married so long they are getting tired of each other.
She even said that he have been secretly talking to an old love from the 90's.My advice to her is that he is bored and he just chatting with her just for fun nothing big.She learned he had 2 mistresses where he lives at in there area. I don't think she should give up.The old time love he is speaking to her on a regular basis whether 3 days go by or not they talk , chat all day long.They even went to the island together for a wedding and he was still texting this old lover. Again he took her to the wedding not the lover. He was sending her photos and everything.When they got back from the island still text the woman she found out. He says they are just friends from back in the day. I don't think it's a big deal. She should stay.

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