First time poster here, looking for some helpful advice because my head is an absolute mess.
I've been with my boyfriend for just over two and a half years. We met at work when he was moved into my department and became close friends rather quickly. He was in a long term relationship at the time which ended horribly not long after we met (he claimed that he caught her sleeping with a mutual friend) and I was there for him and we subsequently got together a short while after they split up.
Everything's been great and last week he asked me to marry him which I said yes to immediately. We told friends and family and everyone was happy for us except for his eldest (of four) sisters who started acting off with both of us. I've always got along really well with her so I found her attitude really hurtful and wanted to speak to her but he said he'd deal with it. Over the last week I've noticed that they've been messaging a lot and he seemed really angry but still wouldn't talk about it.
Yesterday I had enough and rang her. She said that as he wasn't going to tell me, she would because she couldn't believe he was willing to marry me and still not tell me. His ex was pregnant when he left her and he has a baby son that he has never met or had anything to do with.
I am absolutely gutted. I can't reconcile the fact that this man who I love so much, who everyone loves, who is funny and kind and hardworking is capable of abandoning his child. When confronted, he kept saying that he didn't know if the child was his, that he was going to tell me eventually and that if she hadn't cheated on him then he wouldn't have left and I just don't know what to do. He's livid at his sister too but she maintains that she's done the right thing because, in her words, she's 'sick and tired of being denied a relationship with her nephew because her asshole brother was too much of a pussy to be a dad.'
I'm just completely blindsided. A week ago I was picturing my wedding and now I can't even look at him. What do I do? Would it be unreasonable for me to contact his ex? Would it be unreasonable for me to leave him? I just really don't know what to do.