Suggest Treatment For Difficulty In Ejaculation

I find it very difficult at best, and typically cannot at all, ejaculate. I know that is worth a good laugh, but it has become frustrating for me. My partner has been very patient but has endured some soreness. We are in a long-term committed monogamous relationship and have grown closer, more in love, and ever more open to discussing sex and its part in our relationship. Except for me and this symptom we are very happy in our love-making and our relationship. Oh, all is not perfect, but we keep mutually working to improve things. We are both 70.