Unfortunately, the law and woman's charter in Singapore do not protect women the way we all wished it would. And most lawyers, like the few i consulted, will tell you: divorce do not seek to "punish" anyone, even in a proved case of Adultry (with solid evidence from PI etc). The reason "Adultry", works the very same way as "intolerable behavior" and "unconsumamted marriage/no sex", other than a quick divorce, there is no added bonus when you arrive at the stage of asset distributions.
Plus, to add salt to insult, when the hearing happens, if he does not contest the divorce, he does not have to be there (he can just get his lawyer to represent him), but you (the wife who filed the divorce) cannot be absent.
I went through that myself. Speaking from my own sad experience, going through all this, is emotionally taxing, having to repeat how you discovered the affair, when you found the photos and important evidence, how he confirmed the affair with etc to the lawyer and Judge. You really have to stay strong throughout the whole time. I am only concerned about how you are gonna be after childbirth, as women tend to be more emotional and prone to depression post delivery...
I have spoken to another forumer who used a PI to gather evidence, honestly, it is ALL up to luck. The PI she used repeatedly missed out on important chances to nail the evidences, and has a bad attitude when she spoke to him. She spent near $4k on his services and gathered nothing substantial. Eventually she found the evidences herself, through his computer and mobile phone.
As for me, i found the evidences from my ex's digital camera, email accounts and credit card bills... What i mean here, simply is, you just have to stay calm and composed, as you already are, and open your eyes, you will find the evidences you need.
However, do bear in mind, all evidence have a 6 month shelf-life/validity. So do gather as much as you can.
More realistic things you should do now, is actually start spending your hub's money (now you have a good reason... buy baby stuff!!), at best chalk up credit card expenditures if you have his sub-card, and make sure he gives you a household allowance every month (make him transfer that to your saving's account, so you have bank records). All these is an indication of the kind of lifestyle you have during marriage, and IF there is a divorce, he will have to maintain you the very SAME way! {I am an idiot as i didn't do all these and now i have no records that he supported my lifestyle so as to substantiate my application for alimony. )
Stay strong and a big hug for you, i know its tough but you will be an even stronger woman than all of us, for the sake of your baby!