Yes, @Moonchild5, your Partner is cheating.
This drug using, self-serving player has form for going out and not coming home or communicating, even when you’re pregnant, are ill, and have a sick baby. That is appalling. This time you found evidence that he lied about his whereabouts, and in fact stayed in a hotel. He wouldn’t have been alone.
He has risked not only your sexual health, but also your baby’s health in utero.
Your 10 year old has the measure of this low-life, and doesn’t like or trust him. He is indeed a keen judge of character, and he sees P’s contemptuous behavior that devalues all of you.
Surely it’s game over, @Moonchild5. Don’t even give him the opportunity to gaslight and blame shift. (Newsflash: You had every right to look for the truth by investigating his wallet, phone, etc., due to his dodgy absences, disrespectful behavior, and possible drug use.)
Tell him it’s over and mean it.