Advice please!

They say that you should never go looking for something that you don’t want to find.

Well I did and I found something that I didn't want to!

Yesterday started with my first midwife appointment which was probably one of the scariest things ever- the midwife struggled to find the babies heartbeat so I had to go for an emergency scan at hospital – luckily everything was fine with the baby.

When I got home, I logged onto the laptop to find that you partners facebook was logged in…..now don't ask me why, but I looked as his messages.

There was a message from January 2017 from a random girl asking him what he was upto, he replied saying that he was out with his friend, she then proceeded to ask him for a lift to a night club in London to which he agreed. When he got home that night I would have asked the usual unsuspicious "what did you guys get up to tonight then"…..well he would have lied to my face about where he actually was. Since that night there have been a couple more messages, up until January this year (when we were trying for this baby) . Maybe it is my pregnancy hormones but they come across as a little flirty, random kisses, happy birthdays with kisses (he never wishes anyone happy birthday on fb). I feel as though this isn’t the only place they were messaging, but I have no proof.

Last night I sent the girl a message to warn her to stay away from him and he was angry with me!

Basically what I want to know is, am I being unreasonable being this angry with him?