Ladies I need advice

So my boyfriend and I have been trying to have a baby right. Only him and I know and my family. His family doesn't. So little back ground knowledge his older brother "Marcus" has a gf right she already had a baby with some guy ( she doesn't let the baby's dad see the baby even though the baby is now 2) but Marcus and her just had a baby. From the beginning Marcus didn't want her to have it. He cheated on her a month before they conceived. She forgave him and all that. But still to this day he still talks and tries to fuck my bestfriend. His girl doesn't know. He sent my bff stuff like " when I visit Vegas can we have sex one last time" and stuff like " where do u live so I can come by to chill". I kept my mouth shut due to the fact that when he first cheated I kept my mouth shut because my bestfriend told me to stay out of it so I did. He told her not to tell me but of course she did. I haven't said SHIT about this new cheating right. Cause she didn't listen the first time. When she announced she was pregnant he didn't want the baby. I would tell him he was gunna have it cause no matter what she wouldn't abort it, he said he didn't care he didn't have to be in it's life just like his father wasn't in his. So I stayed out of that as well. They gave birth a few days ago to a babygirl. I congratulated them and wished her a health and safe birth. IVE NEVER BEEN RUDE TO THEM EVER. Even when I told him to step up and be a real man I did it respectfully.

So back to the point, some lady mixed him up with my boyfriend Mark (they look alike kinda but Marcus is chubby and Mark is fit) well the lady commented on Marcus post saying " congrats mark" so Marcus said it's Marcus baby NOT marks. He said " the baby is mine Mark doesn't want kids" so i said " you don't know what he wants so don't say anything" and he said " he doesn't want kids ... otherwise he would've had one"

He doesn't know we've been trying even BEFORE they had theirs. I found it so horrible to say I know he didn't know about us trying but it still hurt me. He DIDNT EVEN WANT HIS BABY. But we want one.

I want to say something but I don't want to start something that I can't stop. What do I do? Say something or no?

Sorry if in wrong group*