What does he mean when he says this?

[likeamillpond]

Ive been seeing someone for just under a year and it's getting serious.Serious enough that he wants me to move in with him.
I'm possibly overthinking things, but I need to be absolutely sure he loves me before making such a big commitment.. When pressed, he usually says says he loves me, followed by
''You're my only chance at happiness and I'm going to take it''

Help me understand what's going through his head when he makes that statement? He's said it numerous times.
He's fairly good looking, sociable and has a kind personality, so I don't quite understand why he would think I am his only chance?

We're both mid 50s (if that helps)

What are his very set routines? Are they something that you think will cause problems down the line?

It sounds all about what's in it for him. Someone to keep him company and look after him when he's not well, into his elderly years. It's about him - there's something missing and he's only going to get it from you - what about what he's bringing to the party?!

And what does that mean, that it's all your responsibility OP, his happiness?

Stuff that, it sounds wrong to me.

I know a bloke who on many levels would be a 'great' partner (although I don't really fancy him) and he once tried to make a case for us having a go at a relationship when he was ill saying how it's times like these that you just want someone to look after you (he'd been vomiting and having diarrhoea) - I thought wow, that's some prize to dangle in front of me right there! I don't want to just be someone's crutch or their nursemaid!

Does he possibly mean he's lost chances of happiness in the past and doesn't want to let this one slip through his fingers?

I think he's more setting expectations really. Be ready for oddness (which I know you won't like) and I'm already letting you know that I think it's your responsibility, this ongoing happiness, I'm just a poor victim of my previous relationships, it's all down to you. Oh, and I'm telling you about (in not very great detail) about some of my foibles so that I'm priming you to bend over backwards to accommodate them, with not ONE word of what I'M going to do FOR YOU.

I think much caution and a time limit or non-committal test period where you don't give up your current housing is called for but, beware, he's unlikely to reveal in full his set routines / foibles until you've made the leap....