In marriage there is an acceptable code of conduct (we'll call it "do this or you don't get this")that keeps the marriage strong and together. One spouse can makes life so miserable for the other (physical violence, multiple affairs, etc.) that the only sensible course of action, regardless of how much the offended spouse loves the other (unconditionally), is separation. The guilty party is the one that caused the chasm by their own selfish, wreckless actions and got what was to be expected. Unconditional love by one cannot make up for the lack of love by the other.
The same is true with God. He created us and saw us dying in our sins and loved us son much that He sent us His only begotten Son to take away the sins of the world. This was accomplished by Christ's death on the cross and this was done for all. To reject that ultimate act of love (giving up his life so that others might receive eternal life), causes that same separation. His love for us has not ebbed, we have created the separation by rejecting that love.
Unconditional love does not require two, but the benefits and rewards that come with unconditional love (being together) requires two.