Questioning. Any Advice please.

So my partner and I have been together for almost 7 years now. We have a beautiful son together and are engaged. I recently found out for the first year of our relationship, possibly more, that he still wanted his ex. Sent messages to her saying he still loved her, sent messages to his mates saying that he regretted breaking up with her and sending photos to them saying look what I'm missing. The whole time he did that he had told me he loved me and we were sleeping together. It's made me question everything now, I feel like nothing more then a consolation prize and am heartbroken. I haven't said anything to him but I'm so confused right now. I don't know what to do.