How should I feel?

So my husband and I usually have pretty open communication... No secrets, thumb prints in each other's phones, etc. ... Or at least I thought until this morning! So at like 6 this morning, he gets a message on Facebook, and I try to unlock his phone using my saved thumbprint... Nothing... I enter his passcode, it's been changed! And the message was from another woman... Am I reading too much into this, or do I really have a reason to be upset? He's started picking fights for no reason, and keeps talking about cheating or divorce, but then says he's just playing... And I'm 10 weeks pregnant btw with our second child, we lost our first at 19 weeks!