can you help me in this? this message from a my friend

Message:

i have found my wife cheating with me.
she has talking to other guy without in my known
it has happened 3 times.
i warned her before but she still doing that
we have 4y old daughter and our marriage has 6 years

she did only chat and phone calls with them. no real meet and physical relation.

even i give her every possible happiness.
can you define the reasons behind of this
what should i do now?