Posie, I can see your point, and understand why you've come to that conclusion, however, I think that the two don't necessarily follow on. Just because he's looked at this video, and passed it on to others in his office, really doesn't mean that everything you know about him is now wrong and that he's not the man you thought he was. Though, I can truly understand why you might feel this. I assure you i'm saying this from the point of view that i do empathise with your feelings. I'm not being negative to you or having a go at you. ( just wanted to point that out as it not easy to tell sometimes on here! )
What it means is, that he is a fairly typical bloke, who is trying to be one of the office crowd of lads. what he's done is really not out of the ordinary. I fully understand your feelings on it, and believe me I would ( and did ) feel the same, but, I think perhaps you need to take a step back from it all, if at all possible, and see the bigger picture, if this is going to be an issue in which you examine your whole relationship and decide if its going to continue. You owe it to yourself, if nothing else.
Putting emotions to one side, look at what he actually done;
Looked at, and passed on a video of some work colleagues stripping. - This in itself is just a foolish, immature thing to do, it doesn't mean he's turned on by the video, or that he's using it in ay other way than to laugh amongst colleagues about. It really has no reflection on you, nor does it mean he doesn't like/fancy etc you. Yes, it might raise the question of you not knowing he liked this sort of thing, but in all honesty, I think you'd be hard pushed to find a man who wasn't at least amused by such a video.
posie I just want to pose a question to you. If you were at work, and you were forwarded a video of a couple of the young lads you work with, doing a strip tease, how would you feel? If all the women were passing it round, with the lads consent? I'm fairly sure you would have a giggle with the girls about it. Have a bit of a laugh about it, maybe even talk about it at lunch time with the girls. Is that a fair thing to assume? I can see it happening for both groups of chaps, and girls. It woudlnt' be a bad thing, really just a bit if fun, something to have a laugh about. Do you get my point, that i'm trying to put across really badly!!
I would say that the other things that have occurred are actually far more worrying. Not coming home when he's said he would, this in itself is not a great crime, nor is it a huge disrespect for you, just a bit unfair, as you are stuck at home, not going out in the same way. Also, just plain thoughtless really. not the done thing except as a one off maybe. Is this something he does do regularly? If so, this needs addressing more than the video.
Also his use of drugs. Is this a new thing, or is is something you both used to dabble in, pre children? Who is he doing it with? These things are I think more of a concern.
Men are very visual creatures when it comes to sex, and as such, their attitudes to it are very different to women, who are far more emoitional about it. I suspect you are so hurt by it, is because you know what you might be thinking when seeing such videos. Or what you might be feeling in the same situation. It really is just titillation, by most accounts with men and 'lesbian scenes' etc.
Also, deleting his call log may suggest that there is someone he doesn't want you to know he's in contact with. This doesn't mean it is a sinister thing. It might honestly be, because he knows how you might react to his contact with this person, so to a) save your feelings on something that might actually be innocent, and b) prevent an argument about something that again, is innocent. I know, better to be honest in the first place, but you can see what i'm trying to say.
I can't help thinking there are some much deeper issues going on here and this is the tip of the iceberg. You clearly do have trust issues, as you were looking in the first place. Also, becasause he's been covering up what he's doing, by deleting thigs, implies he doesn't trust you to allow his personal space and a degree of privacy.
Oh, I dont' know if any of what i'm trying to say to you is making sense
I hope that I'm helping you look at it slightly differently, and with a little bit more perspective, so that you can do something constructive with your anger. Just feel for you, having to think about all this, and to deal with it.