summer in singapore?

The following line is from "The Photographs" by Saskia Louise Schafer, on page 171 of Silverfish New Writing 6, edited by Dipika Mukherjee, published by Silverfish Books, Kuala Lumpur:

…"She knows everything?! That we’ve been seeing each other since summer? That I’m here now?" His voice was filled with horror….

"She" refers to his wife, "he" is a man from KL, and he is talking to his lover, "here" is Singapore, where their relationship is based in, and "summer" is apparently a season that Singapore has….