AIBU because I don't want to pay for Partners exmil's shopping all the time?!

[Collywobbler]

My partner and I have been together for 4 years, I met him 3 years after he divorced and he has a child with his exw.

EXW and exMIL slagged me off profusely when we got together for no other reason than they both thought at one point my partner and his ex would get back together. I saw the text messages that were sent to my partner and exmil said along the lines of "shes so ugly I can't believe you've lowered your standards etc" so I have never been a fan of either of them from the start!

Anyway fast forward a few years and whilst they've both stopped slagging me off I still don't want anything to do with them although I never say anything bad about them infront of his dc.

When my partner has his DC we tend to try to do something in the evening like go shopping etc. We were out a few weeks ago and I popped into a clothes shop and picked up a few things. Whilst we were in there exmil phoned to speak to her GC and asked where we were, when she found out we were in this particular clothes shop she asked if we could get her several pairs of socks - totalling around £10 I think it was. As I went to pay for my clothes I was handed the socks and expected to pay for them with mine..

Bit miffed but assumed I would be reimbursed but never was, she apparently never asked who she owed the money to or how much it was..

Second time we were food shopping and she called and asked to pick up x y z and again I ended up paying for it because I was paying for my shopping also and again no reimbursement.

Happened again last night we were out in a particular shop and was asked to pick up things that totalled to around £40. Got to the checkout and I said to partner "that till is free if you'd like to pay for your exmil's items" he looked at me as if I had three heads and said "don't be so tight, just put it through with your stuff!"

I avoided responding because I didn't want to cause a scene infront of his DC but I'm getting pretty fed up of this now I don't see why I should keep paying for things for someone I don't even like especially as I never get reimbursed for it!

I haven't brought it up with partner yet as his DC is still with him but before I do - aibu to say I'm not paying for her stuff anymore especially as its coming out of my pocket??

Exmil isn't ill or disabled preventing her from getting to shops and she earns around 4 times my salary.Sometimes I struggle to make ends meet at the end of the month and these extra purchases every other week are not helping!

What happened OP? Did you talk to your partner?

I'd write a receipt up for all of those purchases, hand it to your partner - and say 'don't be so tight, pay up or bill Ex MIL.'
No way in hell would I be funding EX MIL. Bloody hell, he's an arse for even asking you to be ok with that.

I completely agree with BiddyJ.
Your partner was very rude to you in public. He had no reason or right to call you "tight" for not wanting to spend £70 on someone who is nothing to do with you. It's a disturbing thing to say no matter how "lovely" he seems most of the time. You're very obviously not tight, so it's a worry that he was trying to make you feel insecure and unsure of yourself.
I also agree that he should be organising activities with his son and not laying a guilt trip on you or relying on you to provide love and care. Obviously you want to be there for him, but it doesn't bode well that it's a problem for your DP and his son if you're not - can he not arrange things that his son would be excited about doing with him? He sounds quick to criticise his son's mum for making false promises, but seems unable to entertain his son happily without you, or to even want to.
You sound very kind and caring but your DP is taking you for granted, and there is a side of him that wants to make you feel bad about yourself.
Just be aware of that, and call him up on it if he ever does it again. (Well done for getting the money back by the way!)