I kissed a guy whilst being in a relationship, what do I do from here?

I (25m, gay) was invited to the club by a group of 5 friends, 1 other person in this group is also gay and is a close friend.

I agree to going to the club, as I had not been for a very long time because of other commitments, so I thought it would be nice to let off some steam and enjoy myself for a change.

The night was going great, the drinks were going fast and the music was awesome, as the night continued the group got smaller, 2 went home, 1 got escorted out of the club for being too drunk and another met a different group of friends in a different club and stayed there, leaving the original group of 6 being myself and my close friend.

We continued the night until 4am when the club lights came on and we all had to leave, so we finished our last drinks and left.

Both of us being extremely drunk and no other club open, we began the walk home, this took us nearly 4 hours to get home as we stopped and sat down, we spoke about a lot of things, life in general, going to different countries and trying different foods and then, out of nowhere, it happens, me and him kiss, more than once.

During the kiss it felt kinda passionate from him, as if he wanted more from it.

As a result of this and being mildly autistic, I had a mixture of reactions and emotions to this, I felt the sense of danger, as even thinking of kissing someone else whilst being in a 2 year relationship is something I never thought I’d do, it also felt like a breath of fresh air and something completely different, it was exciting.

But ultimately I feel so much regret, I feel fear as my boyfriend doesn’t know the kiss happened, and I also feel a lot of uncertainty.

For 2 years, I have loved my boyfriend, it was love at first sight, I fell very quickly for him because of his charm and good looks.

For 2 years I have devoted myself to seeing him and helping him through life, we have moved mountains for each other, every day I see him, it puts the biggest smile on my face.

I kissed another guy, that alone is unforgivable and it makes me look like a horrible person, but I truly do love my boyfriend, but because of my actions, I feel like the love is fading and will soon be a thing of the past.

Should I tell my boyfriend what happened on that night and risk wasting what has been the best 2 years of my life, or should I keep it a secret and not break his heart?