Be gentle with yourself. You have built-up your expectations of the time, place, and person you wanted to share yourself with and it didn't go according to plan. Life, love, and (yes) sex, rarely go according to plan.
I'm assuming you mean that you had your first receptive anal sex experience last night. Because you've never done that, expect it to be new...and raise some emotions that might be confusing. Anytime we do something new (sex or otherwise) there's a lot of learning that subsequently occurs.
If I were to make an assessment on what you're feeling, I'd have to say that you placed a high value on waiting for 'the one' to do that sex act with...and now that you have, you feel regret. And you tell us that he is definitely not 'the one.' It is logical that you feel this way. You can modify your expectations, decision-making, and behavior in the future...but what's done is done (and can't be taken back). So, now we turn to how to live with your new reality. This really is good news for you. You're likely not going to commit to spending the rest of your life with this one guy. So, now you can move on to finding 'the one' for you. Continue your search, keeping in mind that you only have to get it right once. Additionally, you now have more information about what your likes/dislikes sexually are...where your boundaries lie. This is important information for you...and for a potential mate.
Again, be gentle with yourself. The only thing that has changed is now you have one more in a series of life experiences that make you the wonderful man that you are.