He often goes out after work - and I never really know where he is or what he's doing. He was out last night until 1am. He only gives me the sketchiest explanation when I ask him where he's been. ie. 'A work do'. And if I ask why he got back so late he gives vague replies like, 'It just really went on. I was chatting.' etc etc.
In the past I've found cards from girls - but it's ambiguous as to if anything has actually happened. And when he comes back from business trips he often has photos of his female 'work colleagues'.
He's a really good liar as I've seen him lie brilliantly to other people. So I don't trust the answers that he gives me. We've been together 10 years and have 4 children. What should I do?