Hi Velvetee, im going to go through your post bit by bit, firstly you lost your mum only 3 weeks ago, so your feelings are not going to be about satisfying yours and your mans sexual needs, that'll be the last thing on your mind, and he should be supporting you through this! Secondly, you may feel unatractive and have your reasons for feeling uncomfortable about sex at the moment, but couldnt you please him in other ways but without penetrative sex? A nice cuddle afterwards and a show of your feelings for him would be nice too.
About him messaging another woman, would you be able to accept it more if he were slagging you off to a man? Not that this makes it any easier, I would not be happy, but I would also look at why he has done it, which I think you have already done judjing by your post, he obviously feels unable to talk to you at the moment, maybe its because of the loss of your mum and now is not thr right time, but feels the need to vent his frustrations elsewhere, we all say things we dont mean when we are angry.
Maybe him going back to his mums for a few days will do you both some good, as your mind will be free from the arguing thats going on at the moment, and you will be able to think about what you want from this...that applies to both of you, you may even miss eachother and realise what you both mean to eachother again.
Sounds like a lot has been going on in your mind recently, and they are major things, which he should try and understand instead of trying to escape you he should be helping you as much as he can...thats what any loving partner would do wouldnt they?
I wouldnt be happy about the things he has done, but I wouldnt be happy if I was him either, I think you need to sit down and work out what you both want from this and work at sorting out your differences...best of luck x