Is my husband cheating? Should I be upset???

Okay so my husband got a present from a female coworker and she wrote a heart on his card tag. She also is the same female coworker that screamed “ty I’m pregnant hahahaha” when I was on the phone with him one day (she didn’t know he was on the phone).

Ok so I don’t actually think he’s cheating but should I be mad about this or just let it slide? I think what I’m most upset about is when I brought it up he got mad and refused to talk about it told me I was insane, had a mental illness, and Hasn’t talked to me for 2 days now, giving me silent treatment 😭. Why not just say it’s nothing and move on???