How do you let go?

My bf just left our apartment 3/4 days ago and is staying at his moms house. We have a 1 year old baby & he knows I depend on him for rent & whatever else we need. Since he’s left I noticed I’m not happy... but why? Cause when he’s home I don’t trust him? & I definitely don’t trust him now that he’s been at his moms house? ITS SO FUCKING DRAINING.. how do I let him go? Idk if it’s because I don’t like being alone but I want him to come back but why?! He probably had sex with another girl again & lying about it. I need help. I need guidance. How do u just let go?