Hi Rav Yaron Reuven,
When I was 17 years old I estimate, I was a "president" of a very popular Kiruv organization that you called out recently (for sending Jewish teenagers to rebuild house of pastor) in my city.
One Shabbat, we were on a Shabbaton. There was a secular girl who took interest in my friend. She didn't speak English though, only Hebrew. I spoke Hebrew. So I was the translator between them.
She asked me, does he like me? How do I speak to him? I said, of course he does, and I gave her all types of advice. I also gave him all types of advice. I'd spend entire bus rides taking to him about girls, and about her.
I went to him that Shabbaton and said, hey she likes you, you should speak to her! I wasn't the only one at work at helping this, but I was definitely part of it. There was another girl that may have done more than me, but I believe I was part of it.
5 years later, they are still dating. I am so scared. I am terrified I was Machtiah haRabbim. Terrified. If I caused the relationship between them... oh my GD. Is my Teshuva almost impossible? What do I do...? I feel terrible.