I had a relationship like 7 years ago, when that relationship had ended.. Me and the guy didn't see each other for like 1 year... But after we began to work at the same place for 2 years.. and from that day till now we were seeing each other sometimes.. but he has an other girlfriend and I'm single right know... But I had loved him from the first day.. how do I know if he feels the same for me? I want him back.. And don't know what to do

Leave people in relationships alone. You obviously need a happy life outside of work.

Just be honest and ask him what he wants to happen. If he has a relationship and is seeing you too you also have to think that you could be next for being cheated on. Its up to you to choose what path you want to take. However stayimg away from him sounds like it would be safer.