I think my so is cheating....

So my SO has been extremely obsessed with his phone and always tells me to lose my attitude even when I don’t say anything. It has now gotten to the point where we don’t even very rarely have sex.

He tells me he’s going to see his mates or has to go help someone out and is gone for ages and when he comes home he’s a totally suck up, like he’s been somewhere he shouldn’t. A few times I’ve actually caught him out not being where he said he was but he just tells me some other bullshit story or makes out that I’m being dramatic.

He has Snapchat and recently he has turned his snap notifications off and if he’s in it when I walk past he very quickly exits out of it...

Am I looking too much into this or should I be concerned? I have been cheated on with my previous partner so I feel like I know all the signs...

UPDATE!!

If I do leave how do I go about it when we have a 7 month old together, everytime he threatens me to get out he tells me I’m not taking her with me. I don’t want the older two to be involved either.. one is mine from a previous relationship and one is his from previous relationship... and I terrified he will try and do something like hurt me...