Advice on telling your SO you were raped

So I was raped some years ago now and I've never been very good about talking about  what happened. Now I'm in a relationship with an incredible man that I love with my whole heart. I'm thinking about telling him about my past (which is huge for me- I've never actually told anyone before). I think he suspects something really awful happens with my ex (the guy who raped me) but I've never been explicit as to what went on. But I just don't know how to tell him and I feel like he should know. We've been together a while now and I can see myself marrying him and having a family with him so I think he deserves the truth. But I don't know how to get the words out. Any advice? Thank you