No negativity please..

How do you explain to your partner that you’ve been with for three months? I’m not sure how to start it because we’ve already had sex multiple times. We use condoms and I take my prescription as I’m supposed to. I know I’m wrong for not telling him but it is SO hard for me to open up about it to my partners. He’s the first after many years and I feel so freaking bad ☹️😞😞