I'm not a solicitor, but my understanding is:
You can't go after half his salary, for that you'd have to apply for a Spousal Maintenance Suit/Periodical Payments, (cost around 3K). Given you've been independent from him for a long time, and it sounds like quite a short marriage, I would have thought that's a non starter.
If he's paying CM, then you can check he is paying the correct amount.
In theory, you could go after half his assets and for some (but not necessarily half) of his pension for the duration of your marriage and co-habiting relationship if you feel you did not get your fair share.
However, a reasonable person would ask "Why now?" and a defence could be 'it was agreed at the time' and they'd have to prove it was/wasn't.
If you didn't have legal advice at the time, then it would help your situation.
Yes, it would be expensive (around 5 - 10k) so you'd have to stand to gain more than 6 - 11K for it to be worthwhile if you do it with a solicitor.
You'd also have to balance it again what it might do to your relationship with him, and also he with your child, and the fact that going to court is stressful.
If I were you, I'd speak to a solicitor and tell them what happened, and they can let you know your chances of success. Most solicitors do a free half hour or so.