Baby's last name

Megan
I am recently divorced because my husband has several accounts in fetish websites and was sleeping with men and other women. 
I am currently 30 weeks pregnant and do not know if I should give baby my maiden last name, which I have gone back to, or still use my now ex husbands name. 
I really do not know what to do about my daughters last name. 
I do have a 6 year old from a different relationship (completely different circumstances) and she has her fathers last name. I don't know if that makes a difference.. 
Any advice would be greatly appreciated, I'm really at a loss of what to do.