bf stays up late to chat to other girls

Everything's been ok up on till last night I noticed my other half had set up his web cam ( bearing in mind it's never been used as he said it's no good). Then he goes upstairs to have a shave which he never does because he knows I like his beard but that's all gone now. So I'm sat on the sofa and he say " I thought you would be in bed by now" . Which made me think even more something's going on, anyway I went to bed but left the bedroom door open. 
And I could hear him chatting away saying things like I work zero hours contract so he can work the hours he wants. But he doesn't work because he's my full time carer. From the way he was talking I know it was a girl and I know he's done stuff like this in the past I just don't have the proof. So now it's making me question our whole relationship 😔 what do I do now?
UPDATE:- I'm due to come into some money tomorrow and it's going to be very interesting if I catch him out tonite
I have a spare phone I'm thinking of leaving on record once I go to bed that will be all the proof I need.
And if I'm right then he's gone but at least I will have the money for me and my son to start fresh 
UPDATE:- 
I did one better and logged on to his Skye and yeap he's been talking to some girl and waiting till I go to bed but been talking to her on snap chat while I've been in the same room. I'm beyond heartbroken 😭 why would he do this to me. We don't have any children together. I have a son from a previous relationship