John 15:10 states "If you keep my commands, you will remain in my love, just as I have kept my Father's commands and remain in his love." This would imply that one must keep God's commands in order to remain loved by him, yet the word AGAPE means a love given by God to sinners whether it is returned to Him or not. I dont understand, which one is it?
I'm not sure where you derived the definition of AGAPE as "love given by God to sinners whether it is returned to Him or not." That is not a definition I recognize from any standard dictionary, though some well-meaning individual may have explained it to you thus. AGAPE is a Greek word that was changed by extensive Christian use (first in Hellenistic Judaism, then the Septuagint or LXX, then in the preaching of Jesus and the Apostles, then in the New Testament, and last in post-apostolic Christian writing). Initially it meant a benevolent sort of love; charitable regard for someone or something; good will towards; preference.
While in the New Testament, there is some development of the word towards the sort of self-sacrificing love that God has for mankind, that is more a product of its use in the NT rather than the explicit use IN the NT. For more on this, see Kittel's Theological Dictionary of the New Testament 1:21 which you can access here http://www.theword.net/index.php?purchase-item&pid=33&aid=5
(under sample 2)
As to your questions, Jesus is not making salvation contingent on command-keeping. That would set this statement at odds with a number of other statements by him and by the apostles. Rather, commandment-keeping is an evidence that we have concern for God's regard towards us. People who don't have the spirit of adoption (i.e., they don't have filial regard towards God) don't care how God regards them. For Jesus, everything about him was subsumed under the heading of pleasing the Father (keeping his commands, saying only that which the Father tells him, etc.); it's all throughout John. If we want the Father to regard us in the same way that he regarded Jesus, there are two ways to do it: 1) obey God's commandments perfectly (impossible, as we have already sinned); 2) hide yourself in Jesus through baptismal faith.