Boyfriends mum is upset that DP and I didn’t spend enough time with her on holiday

This is perfect. Validates her feelings but without your accepting fault.

I would probably reply with something like sorry you feel that way. You were more than welcome to join us on our outings. Sorry we are not pool people.

And then let you DP handle it

You can address this without a full on apology (I agree that, on the basis of your first post, you don’t have anything to say sorry for).

Something like: “DP and I really enjoyed the holiday and thought you had too. We both get a bit stir-crazy when we’re not doing anything which is why we took the opportunity to go for walks. I’m sorry that you felt left out, but that wasn’t at all our intention and I liked spending time with you without all the pressures of daily life getting in the way.”

You just need to chuck a bone to her, IMO, to grease the wheels of the relationship. All the rest of it, about her loneliness etc, isn’t something you should be dealing with, but she’d clearly built up a level of expectation before the holiday which was probably never going to be met.

What would she do for holidays if you didn't go with her?

I think I would go with the kind of non-apology as people have suggested with 'I'm sorry to hear you feel that way' maybe with an added 'we really did want you to join us on our excursions. But as you turned down every invitation, we assumed you were happier relaxing by the pool.'
Ie remind her she chose to be on her own for a large proportion of it.

Great advice. This, OP.

Are you sure she's blaming you? Is she just expressing herself.

Maybe respond something like. Oh I'm sorry that you felt lonely and that this has made you realise you'd like more connection in your life. Is there anyway I can help you get out and meet new people? How about XYX?

Clearly you are not responsible for her loneliness but it'd be kind to help her a bit.

Don’t apologise, she’s being ridiculous. She felt like a third wheel because she was a third wheel. I’d respond along the lines of …
‘It is a shame we couldn’t spend more time together but we just enjoy spending our time differently on holiday. Im sorry you felt lonely’.

Are you sure she is 'blaming' you or looking for an apology? It makes perfect sense that she felt a bit lonely and like a third wheel and it's good that she's realised it's a wider issue. She should be able to share this without you taking it personally (assuming she is just sharing). I would empathise, but not apologise.

Id say 'omg im so sorry. I just assumed you wanted to spend the time at the hotel. You should have come with us when we offered. We really wanted you to! Sounds like a bit of a miscommunication!

Then dont go on holiday with her again

Let him deal with it, don't respond at all.
What did she expect going on holiday with a couple? As long as you didn't actively exclude her (which it sounds like you didn't) then she's got no cause for complaint

I would go with this. I think if it ever comes up again about going on holiday together, encouraging her to bring a friend for company (ideally someone who wants to sit on the beach all day) is the way to go.

Which is why you should just forward the texts onto your boyfriend to deal with and not do anything further.

His mother is a central fact in his life, and he knows her well, whereas she’s only in your life because of the man you’re currently seeing. If you ended the relationship, you’d never see her again. Her sending her son’s girlfriend rather than her son messages complaining about ‘leaving her out’ on holiday is an odd thing to do. I wouldn’t encourage the sexist view that it’s women’s job to ‘manage’ other people’s family relationships.

From your opening post, it sounds more to me like the holiday had held up a bit of a mirror to her re her own life and she didn't like what she saw.

Are you sure she's angry with you and not just venting to you?

If it made her realise that she is a bit lonely in general, maybe she thought it would open up a bit of a conversation, woman to woman?

Not saying I'm right but, if you read her message again through that lens, does it read differently?

It's just that you've taken it personally and as a criticism when she might not have meant it to come across like that.

Just an idea 🤷🏻‍♀️

Is she opening up to you about feeling lonely in her life, rather than blaming you?

I would respond as if that was her gist.

e.g “it must be hard watching your son grow up and coming to terms with change. But be proud of the man and partner that he has become “

Or just be breezy “oh, you looked so serene and composed on your lounger! We had a lovely time and glad we were able to spend it with you, though it’s tricky when we are out-and-abouters and you are a sun goddess. Talk soon xx”

And then proceed with caution because if she was realising her own singledom and loneliness, she should have kept that for her own reflection, or talked about it more objectively. Very intense and needy to text you about it.

Yes this type of response. Acknowledge her feelings as real to her, and focus on the relationship.

agree with this advice.

sensible to discuss it with him first and agree a united position. but you should respond to her directly and make it clear that you have both talked about this so your bf is aware.

You don't need to apologise.

I'd say something like 'thanks for sharing your feelings with me. I'm sorry to hear you feel lonely and seeing DP and I so happy together as a couple has compounded those feelings. If there's anything I can do to support you, let me know. Maybe we could grab a coffee at some point'

Has it ever come up before ,like has she said her son doesn't spend any time with her. She went on holiday with a couple I don't know what she expected to happen . She was invited to go on excursions and didn't want to. Did she think it would be like a family holiday from when her son was a kid? I think maybe it highlighted that she feels lonely and didn't realise

I think this is the kind of conversation you should have face to face rather than by text.
Rather than get into rights and wrongs, I think if bf (and you) can reassure her she is loved and appreciated that would go a long way.

She really can't expect you to just do what she wanted all holiday. She's being ridiculous.
Also her being lonely isn't your responsibility

Your boyfriend needs to have a conversation with her about the fact that she only felt lonely because she refused to go with you, and she can't seriously expect you to sit on the beach all day just to keep her happy. If that's what she wants, she need to find a friend who has similar holiday tastes.

I firmly disagree with the whole let your boyfriend deal with it because she's his mum unless that is the precedent you are happy to set when it comes to his family. Personally I feel it is important to have a relationship with the inlaws independent of your partner. However in this case I wouldn't respond to the text till he gets home. I'd discuss it with him first and then either ring and speak to her together or have her over to yours and speak to her. I also would forget about any discounts she can get when booking a holiday and not agree to a joint holiday again. You made compromises on the holiday but it was your holiday as much as hers.

Did you eat meals together? I guess it depends what relationship you want with her going forward if you want to step back and have your partner handle it then fine but if you want to be more of a close family then you could just say something like ‘I’m sorry you feel that way. I really enjoyed spending time with you on holiday and thought we had a lovely bonding time talking about x, eating at y blah blah’ maybe talk about it more next time you see her face to face

I wouldn't be making use of the discounts again. Seems not worth it for a cheap holiday.