When this happens it is tempting to rush into things. But for now, go 'stealth'. I'm not saying not to leave him, definitely do that! But choose your time wisely. You have assets, at least the £35k. You need to make smart decisions. It doesn't matter if you've been married 3 or 30 years. Anyone with assets of any kind needs to seek legal advice before leaving. He may be 'nice' and let you go easily and keep what you have, or he may be a jerk who will try to make your life miserable and take from you. And make no mistake, ofttimes cheaters turn vindictive. Guilt over their betrayal rarely plays into their emotions, sometimes quite the opposite. He's already put the blame entirely on you because he cannot face up to and take responsibility for his actions. How long before he convinces himself that 'you owe him' for 'making him cheat'?
Make your plans by all means. Call your mum and let her know what's up. Set up a 'contingency' plan with her in case you need or want to leave suddenly. I'm hoping and praying she lives a 'commutable' distance from your work.
Get a few day's worth of clothing and all important papers over to hers, or to a secure location. Do a quiet inventory to decide what you definitely want to keep and what you are willing to give up/bargain with.
Find a new place to live, don't assume that his parents will allow you to stay out of guilt that their son cheated on you. Hopefully his parents will be willing to take you off the lease once you have explained the situation. As far as what they may know or not know, take nothing for granted. Have you noticed them 'pulling back' or felt a 'coldness' from them?
If you have joint finances, keep an eye on them for now. Open a separate account for yourself, but do not shut down joint finances until you have spoken to a solicitor OR unless you see that he is moving money around himself.
All this may sound a bit 'mercenary', but right now you need to be all about protecting yourself.