Hi, I'd like to help you with your question.
There are several signs that a relationship is over.
One, communication slows down or stops- the couple no longer communicates with each other like they used to. They find it more appealing to talk to others outside the relationship than to each other.
Two, spending less time together- the couple feels they'd rather be apart than together. Other relationships seem more appealing.
Three, special gestures stop or slow down a lot- flowers, gift giving, dinners out, etc all stop.
Four, the couple agrees they do not want to be together or need space from one another.
It sounds like your relationship has taken a downturn, but is not over yet. Going through a rough time can strengthen a relationship. The most important factor in getting through this time is communication. Talking out how you both feel and active listening can help you both work out the problem this situation with your ex friend caused.
It may also help to find a neutral person to help you both talk this out. A mutual friend, pastor, or a therapist can help. You can also agree to spend some time apart but use the time to educate yourselves on how to talk to one another and improve your relationship. Here are some resources to help:
Couple Skills: Making Your Relationship Work by Matthew McKay, Patrick Fanning and Kim Paleg
The Relationship Cure: A 5 Step Guide to Strengthening Your Marriage, Family, and Friendships by John Gottman
Why We Pick the Mates We Do: A Step-by-step Program To Select a Better Partner or Improve the Relationship You're Already In (Psychogenetics System) by Anne Teachworth
You can find these books on Amazon.com or your local library may have them for you.
I hope this has helped you,