When is the appropriate time to indroduce kids to a boyfriend/girlfriend?

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My son and his wife separated two months ago. His wife left on a Thursday and by Sunday had a new boyfriend who she found in a bar. Now six weeks later she has introduce him to the kids and 8 weeks spent the day together with the kids. One is almost 4 and the other is 5. The wife now lives with her mother who just separated form her husband/the wife's father/the grandfather. I may be wrong, but I think it is just too much to soon for the kids to deal with. They are dealing with mama and papa, now mommy and daddy separating. The kids are having to get use to staying part of the week with dad and part with mom. The 5 year old cry's when it's time for bed, because she wants her mom. Just not enough time for the kids as well as the parents to get use to the new life style they are now living. Let alone how can she know what kind of person this guy is in just 6 weeks are even if they will have a good relationship. If this relationship does not work in 6 more weeks will she introduce them to someone new? Someone tell me am I over reacting?