My friend doesn't know how to tell her husband the baby isn't his: Advice?re

My friend is in a difficult situation. She’s married and recently had a child. When she conceived the said child her and her husband were split up. When she returned home and they agreed to work it out she was pregnant obviously by someone else. She had intercourse with her husband upon returning and waited to tell her husband she was pregnant as they recently had a miscarriage so her intent was to make sure everything was ok before telling anyone. When she told him she left out the important detail of the child not being his. The other person knew of the situation and agreed to not cause any conflict and allow the husband to be daddy tough decision but the both agreed but if life changed or her feelings changed he’d step up 100%. Well fast forward husband hasn’t said anything but sometimes seems a little skeptical but also gets excited when people tell him the baby looks just like him. The baby is almost 3 months old and she wants the other man to be part of as she’s finding herself struggling and needing help with the said child but also doesn’t have the words to tell her husband who’s trying but can’t necessarily provide the support she needs because of his work hours. Side note the baby looks almost identical to the mother but is slowly changing and showing some feature of the dad. She wants to know if she should say something when to say something and if so how she should go about it I’ve tried to provide support but Im not exactly sure what the right answer is I feel it’s going to hurt either way. Help Mamas Uncut !!