You're young, no
children to consider & you have the security of being able to move back to your mum's.
You've been in bad relationships & you sound close to your family.
So as long as you are sure within yourself that you'd be confident enough to walk away if tings turned bad - then you have nothing to lose! Go for it!!
In the past I've been on both sides of this (But not as wealthy as your boyfriend!!) At one time I had my own house & the bloke I was with was lodging elsewhere. I asked him
to move in with me as it suited us both. He was just getting back on his feet after a
bad time & I was managing fine before he moved in so I didn't need a financial contribution. I just wanted him there!
Another time I met a guy when we were both on a course overseas (Where I was living short term) . We talked a lot & he travelled out a few times. We wanted to be together & he was in a good job (I was working, but working & travelling) so he asked if I'd move back to the UK & live with him. He knew it was a big sacrifice of my lifestyle (& couldn't do the job I was doing there, here in the UK) and he said he was happy to carry on paying the bills as he just wanted me there! (And other than a bit of food, I wouldn't be costing him anything anyway!!).
Life is give & take and money isn't everything.
Do as he's said, put what money you can aside for A property if you ever want to buy one.
Who knows this may turn out to be an amazing relationship and you may never move out.!!
Also, you can't keep up with his spending, so don't try! Don't spend more on a night out than you would if you were going out with friends or on a date. If he wants to spend £300 on a meal, you don't have to pay £60 for travel/drinks. Your income probably doesn't support that kind of expenditure whereas it's small change for him - and if you'd be happy with being at home or a cheap meal out don't feel compelled to over spend!!