DISCO you put into words what wasnt right about OP story for me.
It is sort of intimate to wear a mans shirt/ T-shirt in bed. I do think also that sometimes (back back flamethrowers) some ex-wives play mind games - I have had experience of this and my DH is a head in the sand type - clueless and oblivious to it. I knew it was going on but knew he didnt see it.
My DHs EXW came to ours when we first moved in as her DS lives with us - adult btw but as she lives long distance we were just being reasonable in letting her visit her DS in what is his home - I suppose. Would never ever let her sleep btw - was only ever mentioned by DH in a jesty way once and I absolutely blew it out the water - never to be mentioned again. But thats just me.
She came in and was just too comfortable IYSWM - she actually sat on the lounge carpet when DH popped out and had her other son - older who lives nearby and visited at same time { oh yes my house was her 'meeting place' also !} - sat on settee above her. Her other son (our resident) sat opposite - and I was sat to one side on other settee. I could not believe she sat on carpet - and fact she was flanked by her two sons made me feel so marginalised and outnumbered in my own home.
DH and I werent married at time - not even discussed it so I think that made her feel of more importance than me - even in the house DH and I bought together ??. She would act as if she had a right to be there -because her family was there - even walked in a couple of times.
To give example she said to oldest son ( ONE WHO DOESNT LIVE WITH US !! ) - 'I need to make a phonecall' - and he said - 'Oh use Dads he wont mind - its free during the day' 
!!!!!
I'm sat there thinking am I invisible here ? - who's house is this ? - so I said - 'Yes - it is free - use my phone by all means ! '
So she then - sat herself right in middle of lounge carpet now and pulled phone by its flex in front of her.
While on phone she was asked her name and right at the moment she said it she looked straight at me and said - 'MRS DHsSURNAME'.
No-one can tell me thats not mind games - it does go on. I could not convince DH of it he just didnt get it - like 'uh - oh she's always sat on the floor and she still uses married name cos of kids' (both adults btw).
Apparently I was being a nutcase - but years later she got thrown out by DH and asked who she thought she was turning up unannounced. [evil
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I'd come in from work and her handbag was on the settee and she was talking to her son in his room. Unbeknown to her that day we'd had worrying news as I'd had a cancer scare and instead of getting all clear had been called for further tests. All I wanted to do was get home and as soon as DH got home - tell him and throw myself into his arms - as you would !
Instead I rang my DH - who was usually home around same time - and screamed at him down the phone - 'Where are you ?' - and no I've not got the all clear - and when you get home before you come upstairs to me - GET YOUR FUCKING EX WIFE OUT OF MY HOUSE'
So he did ! She got all indignant with him and had attitude that she was 'entitled' to visit her son and why should she give us notice etc etc. She even refused to leave.
So I'm afraid I'm biased towards OP being a terratorial thing really from my own experience and I would make it clear to DH just in case this is whats going on - he is careful not to 'aid and abet' her or you will review your sleeping over stance.
Sometimes the more tolerant you are - and you definitely are if EXW sleeps !! - the more people expect you to be - and that leaves others free to push the boundaries. IME this is what happened with a 'head in the sand' DH and a cocky EXW.
BTW got all clear eventually and EXW now meets her son elsewhere when she visits. Saw her arse and never been near since.
RESULT x 2 