With slight modification your code works just fine:
ggplot() +
geom_point(mapping = aes(x = X, y = y)) +
geom_abline(aes(colour = "line_1", intercept = -0.9930872, slope = 0.4866284)) +
geom_abline(aes(colour = "line_2", intercept = -1, slope = 0.5)) +
scale_colour_manual(name = "lines", values = c("red", "blue")) +
theme(legend.position = "bottom")
Added legend position in case if you want to change that aswell.
solved Add regression line legend to geom_abline