When me & my boyfriend started texting each other basically novels back and forth in the beginning of our relationship, we got on the subject of either medications or mental health (this was quite a while back so I can't remember which), since he had experience with anti-depressants & was diagnosed with ADHD, I guess I just felt safe telling him about my own issues? I know I definitely had a "this could ruin everything we've basically just begun" feeling after I hit send but I already knew what a compassionate & understanding person he was so I figured if he couldn't handle this than it wasn't meant to be. He's handled all of it super well, and I'm thankful as hell to have him both in my life & as one of my go to people when SHTF.
If I had to choose how to tell him again, I'd probably opt for in person just so we could really TALK about everything. But it was nice to text it so he didn't have to see my emotions or watch me stumble over phrasing things correctly.

Honestly, it's not something that you can really "get over" in a relationship though, just like no one can get over a mental illness. You will have bad days, and your partner will notice. They might go for a silently strong approach & support you while waiting to see if you bring it up, or they might become really concerned & want you to talk about your feelings with them. Their concern might even annoy you (I know sometimes I DON'T want to talk about what I'm going through, even with the people I love most), but it can also be comforting to know that they're there & only want the best for you.
In the end, it's a very personal decision only you can make, if you don't feel ready to talk about it yet, don't push it! I'm sure if this person is someone who is meant to have a place in your life, they'll be patient and understanding.