If something is bothering you, you have every right to confront whatever you like. Normally things are better confronted in the moment however, it's still on your mind. What are you looking for from doing it, may I ask?
Do I need to just put up and shut up now? No Has too much time passed for me to be able to confront him about this now? No Where do I go from here? Depends really. He is obviously a serial cheater. So do you want to be in a relationship with a serial cheater? Always worrying if he's lying or hiding something from you? Always worrying he's having sex with other women or looking for women to sleep with? Run the risk of getting an STI because he may have caught one from another woman and given it to you? It depends whether you love him and hate yourself enough to live with all that.
So, he cheated on you for the first 4 years of your relationship, and you are considering sweeping that under the carpet?
And I agree with Imperial - he figured out how to go Incognito in 2013.
Can you access his e-mails and his dating profiles? That would show any recent activity. If not, I'd set up a fake profile on one of the sites he is on, and then I'd send him a message chatting him up. Try to trap him.
He'd be out on his ear before teatime, if he was mine.
He's been doing this a long time. While he's with you. People don't change that much over time. Unfortunately, the web is full of places to do this - Whatsapp, Skype, even an RPG I've been on for years is full of sad people going into the chat rooms for that purpose.
The question is, bearing in mind there's no real way to keep tabs on what he's doing, are you willing to put up with constantly wondering?
So he's been taking the piss since the whole of your relationship and you've never taken him to task but you want to now - wow, can't believe you have allowed him to get away with that, and web camming, eugh, disgusting.
I'd guarantee he hasn't stopped OP, you gave him the green light and have done nothing about his past endeavours.
What's to confront, he cheats, lies and tells you it's a laugh - you don't need any proof or denying, you have to decide if you are happy to continue in a relationship where the man is showing you zero commitment.