Dear Kaylee92~
First of welcome here to the forum and congratulations on your 3-month old. Being a new mum is strange territory for anyone, and books and so on are not all that is needed. It is natural to worry if you are doing the right thing all the time, that your baby's health is good and nothing goes wrong
It takes a lot of getting used to (and a lot less sleep :(
I would hope you have some support for your new motherhood, my wife had her mum who was experienced and on hand to help - do you have anyone like that?
Now the uncharted territory is living wiht someone you love who suffers depression and has been suicidal. Worrying about is state, and worrying if you are going to say something out of line (you are not) is exhausting
I think it is a tribute to the love between you that he opened up and said how he had been feeling all the itme and about his attempt.
That is a really big plus.
I was in that situation and did not open up for a very long time, which simply made things harder. Though when I did open up -and it was to my wife too - that was the start of things gettng better.
That happened for me with medical help, I saw a doctor then a psychiatrist and treatment began.
Has your husband got medical support? If he has then he needs to have a serious conversation with them , their regime is not working and needs a review. They also needs to know about the suicidal thoughts and attempt.
If he has no medic support now is he time to get it -even if it is hard for him to tell a doctor all about it, it needs doing, and like me will find the path gets easier.
Does he have anyone he can talk with apart from yourself? While that is excellent it does place an awful lot of burden on you.
How to help? Well just listening, showing care and assuring him you will always be there for him, plus praise, is fine. If he would help with the baby that would be good too, though without pressure.
You can help him make a safety plan like I have. It is free, fits on a smartphone filled in in advance and you reach for it when frightened or overwhelmed
Apart from the usual emergency numbers and people it has room for all sorts of things to give a lift or have made him happy in the past. As I found them hard to remember so I needed my wife's knowledge of me to fill it in properly. Everything from You-Tube clips to pets and music
https://www.beyondblue.org.au/get-support/beyondnow-suicide-safety-planning
I'm out of room, hope you come back and keep talking with us
Croix