If two Christians are friends and commit adultery with each other and then repent of their sin of adultery can they still remain friends? Can they be restored to a chaste, pure relationship with each other as brother and sister in Christ?
I believe it’s possible to accomplish what you suggest, but only under certain conditions. It takes a very strong commitment on the parts of all parties involved. The fact that you call your sin adultery instead of fornication indicates that at least one of you is married. That complicates things substantially because it means that betrayed spouses have to agree to accept the ongoing relationship, something very few could do. If that’s the case, I don’t recommend trying because it really isn’t fair to the spouse(s).
If you simply used the wrong term and you’re both single, then you have to make sure there’s no ongoing sexual tension between you. You both have to be more committed to the integrity of the friendship than satisfying your sexual urges. I take it that there’s no romantic involvement between you that would lead to you eventually becoming a couple.
I would suggest bringing a trusted third party (also a believer) into the picture to help you transition back into the brother/sister relationship you’re trying to restore. Agree that the two of you won’t be alone together for a while and ask the third party to chaperone you and observe your interactions with each other to keep you accountable and make sure you’re not kidding yourselves.
So if you’re both single, if your sexual involvement was just a lapse of judgment and there’s no lingering feeling of that nature between the two of you, if you’ve sincerely confessed your sin to God and promised each other before Him that nothing of that sort can ever happen between you again, and if you’ve established the proper accountability, then you have a chance of restoring your chaste relationship.