How can I tell Him without telling on myself?

Question

So my boyfriend and I have dated off and on for about 4 yrs. neither of us were looking for anything serious so we became really good friends in between dating off and on. We started dating more serious recently and became an official couple around September. At this time he also finally got the nerve to tell me that he has a “possible” 3 month old son. I was hurt but couldn’t really say anything since we were never an official couple. He says he never dated her they only had sex a few times. I chose to stick it out with him. He told me that she says that it is between him and another guy, but they both seem to act like it’s more of my boyfriends baby than the other guy’s baby. She also says that the other guy knows but is NOT involved and doesn’t seem to want to do anything for the child. My boyfriend stepped up and is spending time with the baby and buying clothes and things that are needed. They discuss co-parenting and sharing time. They are suppose to get a DNA test after she gets her half of the money but we are working on 5 months here now. My boyfriend has bonded and takes the baby twice a week now. I have never laid eyes on the baby’s mother so i got curious one day and searched for her on social media. During that search i figured out that she knew a few of my family members so i became more curious as to if she was involved in my family somehow.  I googled her name and a baby registry came up and it had her and a baby’s father’s name on the registry with hers and it was NoT my boyfriend’s name. I became even more curious and made a fake account 😜 on instagram and requested to follow her. She accepted and i immediately saw Christmas photos of her a guy and the baby. They even had a family hashtag. Her friends were commenting on her photos about how the baby looked so much like her and this other guy and she was agreeing. I realized this is a bf that she has had for years that she was obviously cheating on. My bf was told that  the baby doesn’t have a father figure in his life but him so he stepped up even more even though he didn’t know for sure if he was his. i got angry because my boyfriend has been doing a lot for the baby and she calls and asks him for money at least twice a week. I feel she is using him for money. This guy and her even had the baby shower together. Why is she lying? She could’ve said it’s between you and my bf she does not have to lie. They could’ve gotten a dna test and moved on. But now that i know this i really want him to know that she is playing him and this guy is there being a father to the baby but i don’t know how to tell him without telling on myself that i was snooping really hard. Should i not care that i snooped and tell him anyway or should i slip hints in without telling the full story? What if this guy sees my bf taking the baby out of the house and gets mad because he doesn’t know who he is? It could be a bad situation.
UPDATE: 
I told him a day after I posted this and he was not mad. He actually thanked me for finding out and telling him. He actually complained that I waited a couple days to tell him. He pulled back on doing certain things for the baby and is just going to take the test soon. Thanks for the advice everyone!

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I’d tell him and let him know you were curious so you looked because you don’t want him getting hurt by her anymore than he already has. Show him the proof and let him start to separate himself from her and the baby on his own. If not she’s going to keep using him and getting as much as she can out of him.

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my my what information you’ve stumbled into!! that’s a gold mine and I can say why you want to tell your boyfriend. Since she knows some of your family could you maybe say that that family member mentioned it to you and you felt that you needed to tell him?

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You should definitely tell your boyfriend. I think it’s reasonable to say you looked her up being curious and that you came across all these posts with another guy claiming to be the baby’s dad. If I was you I’d say that you’ll both pay for the whole DNA test. You want it, she doesn’t. She will never get her half of the money.

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Just be honest with your boyfriend, it’ll make life a lot easier

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You should definitely tell him! You only scoped because you care. I don’t think he would be mad or upset tbh if anything your helping him get to the bottom of this 🤷🏻‍♀️ he does need to get a DNA test done though. Just to make sure

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Maybe you could tell him that you're curious about her so you are going to look her up on social media. Or say you're going to add her to see baby pics. 
Then say you found those things after. 
Honestly I've done my fair share of social media creeping and I would admit it to my SO in order to tell him about this. 
I would pay for the DNA test and/or not give anymore money until you know it is your BF. Also if it is, the boyfriend needs to know. Not from you, but your BF can't keep this up while another guy thinks he's the Dad, even if your BF is.

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I would tell your boyfriend to pay for the DNA test.

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Just tell him it the way you told us.

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Thats a big secret to keep. Just lay it out for him. There's no reason you wouldn't get curious who the mother of your boyfriends baby is. And there's no reason you wouldn't keep digging once you got suspicious that she's playing him. He might get angry, but he'll be a hell of a lot more angry if he finds out you lied about how you found out, plus the bigger problem is how badly he's getting scammed.

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I would tell him immediately. and tell him and show him what you saw have him stop buying things until he's 100 percent sure it's his. I won't mess around