I am baffled by some of the posts here.
OP is obviously reasonable to decide to end her marriage if she really does hate her husband (whatever the reason/rights on wrongs by either party). Given the situation as she portrays it, she would be entirely unreasonable to have another baby with him. And entirely unreasonable to look to jump straight into another relationship and have another baby as soon as physically possible- she has her daughter’s wellbeing to consider.
A baby should not be brought into this situation, they are not a sticking plaster for a woman’s mental health (wanting a baby may be a significant factor, but I am absolutely sure it is not the only issue)- and OP’s is clearly not in a great place. Having a baby will not fix her problems, it just makes them more complicated. And why on earth would OP want a baby with a man she says she hates? One who clearly does not want another child and whom she states has been actively horrible to her? I mean, who in their right mind would bring a baby into that situation? Nobody with any sense, which makes me think that OP is not in the position to be having another baby. She needs to work out what she wants (other than a baby) and sort herself out before jumping into a new relationship and another baby (or going down sperm donor route)-for her own sake, and most importantly for the sake of her 7 year old daughter.
Either her husband is awful, and she needs to leave him because her marriage has failed, or he is good enough to have another baby with and so cannot be as bad as portrayed. I am not sure if he was always stringing OP along or simply changed his mind. The latter happens, it may mean the couple are no longer compatible, but it is not a heinous crime. And no-one should be coerced into have a child they don’t want- it is often the child who suffers most in those cases. I also think his income being lower than his wife’s is neither here nor there in that situation (just as if the woman had the lower income, it does not make her duty bound to provide a child if her husband demands it).
Clearly, if he was always lying to her that he wanted another child just to make her stay that is an awful, cowardly thing to do- he should have told her up front and then she could have decided what to do with that information (i.e. did she love her husband and the family they had created more than she desired another child). But we actually don’t know that happened- even if OP thinks that, sometimes anger and grief make us see things that aren’t accurate because it is easier to be angry/ascribe malicious motives to someone, than deal with the situation.
I also think OP needs to step back from her desire for another baby immediately and consider the practicalities. Ok, she can afford another baby (but she should remember that as she is the higher earner, and assuming custody of their daughter is 50:50, that she may end up with less than a 50:50 split of marital assets)- but that really is not the only consideration here, is it? Is she mentally strong enough? She is clearly highly distressed and if she is crying every day, possibly depressed, and leaving what has turned into a toxic (possibly abusive) relationship by her account. Jumping from that, straight into a new relationship is not a good idea for anyone involved- not her, not the new partner, and certainly not for her daughter. Going down the sperm donor route removes the partner issue- but again, she needs to be in a better place mentally before trying to tackle being a single mum to a newborn with a 7 year old who has just had a lot of upheaval. Even with great support, that is going to be tough on her and her daughter.
She needs to consider the impact of all of this on her daughter too- she absolutely should not stay in an unhappy marriage for her child’s sake. But, realistically her fertile window is narrowing. If she does not want to go down the sperm donor route, she is going to have meet a man who is keen to settle down and have children pretty quickly. She is then going to have to introduce him to her DD far more quickly than is likely to be advised, and likely to have him live with them. And very soon after, introduce a new half-sibling into this mix. Is that really in any way in this little girl’s best interest?
OP has to consider the wellbeing of her daughter, which is more likely to be negatively impacted by all of that than by the hypothetical worries that she will be damaged by not having a sibling or possible nieces and nephews in the future. Most single children are absolutely fine, and if they aren’t, usually it is not solely the lack of sibling which was the primary issue. Children whose parents jump from relationship to relationship, introduce new partners to quickly and try to rapidly blend families without due consideration and groundwork are generally far more likely to be damaged by that, than by being an only child.
It really is not as simple as “dump him and have a baby with someone else”.