Complex sentence: As he is standing at the water, he drops a glove that Sandra had bought for him and realizes that, in Sandra, he has found someone who loves him and with whom he can build a decent life.
Split into simpler sentences: As he is standing at the water's edge, he drops a glove that Sandra had bought for him earlier. Leonard realizes that he has found, in Sandra, someone who loves him and with whom he might be able to build a decent life.