<human>: I desperately need help and advice with no one to turn to... 

Husband/SO (35M) and I (33F) married for 8 years, together 13 years. We have a 3 year old daughter and a one year old son. 

SO is often on business trips abroad (about 2 weeks every 2 months). 

His email is the default in our browser and I'm often too lazy to switch to mine. 
That's how I found out. 

He put up an ad on Craigslist about how he's lonely in a hotel and wants sexual partners. 
He got a reply from a woman, answered back and she hasn't responded (so I'm guessing nothing happened yet).

This made me reflect on myself and our relationship - in plain words, I've let myself go after my first child. I'm talking about gaining about 35 pounds. 
I'm aware that I don't look as good as when we got married. 

Also, the kids were a significant change in our lives. 95% of our conversations revolve around the children or every day errands.

In addition, due to sleeping problems with our daughter (and again, our laziness, I know), we haven't been sleeping in the same bed for a year (SO sleeps with daughter, i sleep in guestroom).

However, we hardly never fight and have (what i consider) good sex once a week. 

I have no idea what to do. 

Should I confront him? how? Maybe it was a one time thing (I did found out about it in just a few hours) and I should just let it go?

Can you succinctly summarize the text in 1-3 sentences?
<bot>: Husband posted M2F ad while on a business trip, it made me think our relationship isn't solid at all. Don't know what to do.