I just want to know how people feel about this, would you consider talking to other girls behind your significant others back a type of cheating?

Long story short- kinda lol

My SO’s been acting kinda off lately and I have a pretty good intuition when it comes to stuff like this and I’ve had my share of cheaters in the past so let’s just call it a gut feeling. Anyways, I ended up getting snap chat to send recent chat history ect and turns out, I was right. Now I don’t know what was said. however, I do know one of the people was someone who posted sexual things of there body... I want to know if I should feel upset and betrayed the way I do or am I overreacting because physically he didn’t do anything...

I guess the part the hurts me the most is I crave the conversation we used to have, the way we used to be, the connection that was there but now isn’t. I just miss it... and he know that so why would he turn to talk to other girls when he has me right here in-front of him? I just don’t get that and I’m torn right now. we’re expecting (17 weeks) and tried so hard to conceive so why would he have a child with me if this is how he wants to act? I tried to stay as calm as ever when I approached him with this new information and I just sent him the pictures of what I had and said if you choose to lie then that’s on you but if you care about this relationship you won’t lie and you will talk to me... we didn’t get much talking about why and who they were, what was said... just a lot of apologies and he started rubbing and kissing my tummy and it just made me cry because I’ve wanted that... the affection, the support, just him actually knowing that I’m carrying life but he’s never done it... until now. And it hurts me because I just don’t know where it all went wrong...

I’m so confused right now and I want to talk about this with someone and I can’t, I don’t want to bring family or mutual friends involved