Is it bad when a mother wants to spend more time with her soon to be third husband than her two kids?

Ideally a parent would pay closer attention, but it would seem this one can see that her children are fast approaching a time when they won't need her so she's planning as to not be alone in the future.

It's normal for her mother, i guess.

If she came out of a stale marriage, and wasn't feeling the closeness or affection from her husband for a long time, she's probably felt like she has lacked a lot in life for a while. And sometimes divorced people do become totally involved in a new lover.

I don't think there's anything wrong with having a new love of our lives, but our minor children still need to remain our first priority and responsibility.

what your gf's mom is doing isn't exactly "normal" but it's common behavior.

She should tend to her other two husbands as well

It is not bad. Mom is trying to piece together a new and perhaps better life with number three. And to do that right she has to give 110% and he has to do the same. That is they both have to work at it to make it work.

And the kids, you and sis, have to respect that. Be thankful for the time mom can give you. And in fact, invite mom and number three out on a double date sometime with your girlfriend. Mom would appreciate that I think.

My mother was that way when she had a man in her life. Now she's 80, we're all 50+ and she's alone, wondering why we don't have that magical close family. It truly never occurred to her that as parent, she should have been the one to lay that foundation.

That doesn't seem right to me. A mother should care more about her children than her soon to be husband, especially her third husband.