Help for best mate?

Your mate doesn't know the child is not his, and neither would you if you were in his place. Suggest he gets a paternity test as that might soothe the pain, but also point out that if his girlfriend is cheated on him before, she will cheat in the future so if he is willing to overlook the past affair he needs to be ready to look over the ones in the future too. Don't let his love blind him from reality.  As to those who advised you to stay out of his business, that may be valuable advise for other who are NOT close friends, but you are.  It is your responsibility to help him protect himself.

He hasn't asked you for any help. You're welcome to worry as much as you like but the pregnancy issue is between him and his GF only. If he asks you for help, certainly go ahead and do what you can. 

maybe you should get a dna test done

Do you think he's really going to want to hear your unsolicited advice?  Keep your mouth shut unless he asks for your opinion.

Sadly it IS none of your business. Yes, you are entitled to an opinion and you are probably correct - but he is looking for sympathy at the moment and you are there as his shoulder to cry on. He may well consider DNA testing as time goes on. He may get sick of worrying if she's cheating. She may be cheating and may latch onto another guy and you will be there to pick up the pieces when your friend gets depressed. Stay neutral. Stay friends. This is HIS life and you can't run it for him.

You should tell your bro to get a backbone, leave the relationship RIGHT NOW, and demand a paternity test IN WRITING stating he knows for a fact she’s been cheating and the child is most likely not his.

Your friend doesn’t necessarily have to listen to you, but I think if you tell him persuasively he probably WILL listen. And it will be the best favor you ever did for him

It’s something he needs to take up with his girlfriend.  If he thinks she’s cheating, he needs to talk to her about it, and get a DNA test done once the baby is born.  Assuming that it’s his child, he’s obviously willing to do his share.  But if he’s not the father, he should not be on the hook for child support.   In that case, he should show her the door, and she’ll have to go after the father.  Nobody should pay for someone else’s mistake

You can't fix stupid. I'm sorry for your friend,  but he knows what he's getting into. I hope he enjoys paying child support, because if she's having an affair now, she'll  hit the road after the kid is born. After all, she'll  have a nice income coming in every  month. If he's smart, he will get a DNA test done on the kid first thing.

How about you and him take up Praying to GOD!  

He sounds more to me like someone wanting to Run from his own responsibilities!  Have you ever heard of anyone being very pregnant and going out and having sex with others? What risks would this have on the baby to be? 

Is he only a very lazy, devil follower? 

if he really is your friend, you need to trust his judgement and respect his decision about this girl, whether you agree with it or not. he's a grown man. go get a love life of your own. and BTW, how would you feel if he told you how to live your life?