Online, we rarely get a full picture of what does work, only what is not working in the relationship and that can skew opinions, but there is so many issues here -
He is still against it but has said he would evaluate things in a few years, but has said he would only ever agree to one
You've been together for a long time, so I wonder how much time you have for him to 'evaluate things'. I don't think he will. If he really wanted children, you probably would have seen a stronger indication before now. There is a possibility that he thinks that if he waits long enough, you will eventually lose your need to have children and you'll forget about it maybe. Or, if he waits long enough, he can make an attempt at trying for a baby (maybe) but by the you'll be infertile and you'll decide to stay with him anyway.
He said to be before that if he was to have a child and if it was gay/transgender etc then he would not let them be themselves until they’re 18 and can move out
It's interesting that these two things are lumped together because they are not the same. Sexual orientation is not the same as being trans (which carries with it the possibility of embarking on a damaging or dangerous, often irreversible medical journey). For that I don't blame him for making them wait until they're 18.
He is all about work and saving money, which I know isn’t a bad quality to have, but he never wants to go anywhere or do anything
If you were really poor, that would be one thing, but I note that you say he never wants to go anywhere or do anything which implies a personality difference. Some people can make this work but most can't I would say. It will be very lonely for you to always have to take the children out alone. Their enrichment will probably be seen by him as superfluous and unnecessary. I don't think this was the parenting life you dreamed of is it? Those kind of posts pop up here occasionally - women whose partners won't even go to the park with them. Never want to go with them as a family anywhere.
If we have a child later on in life then we won’t be able to travel or do things then, so what are we doing now?
That's your dream, not his. A big mismatch again there.
I’m a free spirit and at the moment I feel like I’m stuck, playing a role that’s not for me. Keeping the house tidy, cooking, all while working full time. And never doing anything fun. (I have started to do more on my own but my anxiety stops me a lot of the time)
I find this a bit concerning. If you are doing the majority of the housework and he's not doing anything, that's one potential problem, particularly the 'playing the role that's not meant for me'. I don't think there's anything wrong with it per se, but have you really thought about the utter drudgery of motherhood? Most children need stability. The days where you feel like you can really sit back and enjoy the colour, fun and glitter will probably be there, but limited. You will hear the same tunes, might have to watch the same children's shows over & over again whilst pretending you find it as interesting as they do. You will have to pretend you are engaged when you are really bored. A lot of parents are very tired, especially in the early years.
I also struggle a lot with my mental illness and have had a lot of lows. He is not very supportive and doesn’t understand it at all.
My depression has a lot to do with the fact that I’m not happy in life
If this is something quite inherent to you, then this is why its extra important to have father that's full on board with raising children. However, I do hope that you are not thinking of having children in the secret, deep hope that it will make your life better. It might, but it might also stay the same or get worse.
Another big thing is that our sex life isn’t great. He’s never really had much of a sex drive whereas I’m quite the opposite. It constantly makes me feel like I’m not good enough or not sexy enough. I do tell him this and suggest we try new things but he doesn’t want to
He is not a sexual person and this situation would be enough to put a strain on most marriages. What was he like in the first few years? Was he always like that?
We do love each other, he’s my best friend and it would honestly crush him if I left. But I can’t hold someone else’s happiness before my own
Do he love you, romantically, or is it more a case of wanting to keep you around because you are comforting for him, and provide him with the emotional support that he wants?
We own a house together and it causes me so much anxiety about leaving and separating all our things
It would for most people. My practical advice is to buy lots of flatpack cardboard boxes. The last thing you want when you're moving is hanging about trying to find extra boxes or trying to shove too many things in boxes that weren't designed for that weight, and then break under the strain.
I have spoke to him about all of this but he is not willing to change or he takes things too personally. He usually gets angry and shuts down completely. I feel like a lot of our issues aren’t fixable and it’s just because we are so different and have grown a part over the years as we’ve grown up
It does seem like you both have developed very differently to each other over the years. I don't blame you for feeling distressed at the thought of breaking up for so long. Maybe ask yourself if you want to be in this exact scenario, same relationship, in 10 years time? How about 20 more years of this?