with draw_line3d it is drawn every frame which you won't want to do with a bmap, you'll need to create the bmap once and set it in place then just update it when necessary.

here's a revised(new) code for drawing between the two nodes which should not be called every frame!
Code:
var var_bmapWidth = 8;

ENTITY* ent_node1; //temp for demo
ENTITY* ent_node2;
ENTITY* ent_node3;

void theil_line3d(VECTOR* vFrom, VECTOR* vTo, COLOR* color, var alpha){
	
	VECTOR v;
	
	vec_lerp(v, vFrom, vTo, 0.5);
	
	you = ent_create("esper_drawline.bmp", v, NULL);
	your.scale_x = vec_dist(vFrom, vTo) / 16; // change to bmap_width!
	
	vec_set(v, vFrom.x); 
	vec_sub(v, vTo.x);
	vec_to_angle(your.pan, v);
	
	your.pan += 90;
	your.tilt += 90;
	
	
}

void main(){
	
	level_load(NULL);
	
	ent_node1 = ent_create(CUBE_MDL, vector(100, 100, 0), NULL); //node from
	ent_node2 = ent_create(CUBE_MDL, vector(250, -75, 0), NULL);
	
	ent_node3 = ent_create(CUBE_MDL, vector(400, 30, 00), NULL);
	
	vec_set(camera.x, vector(260, 15, 400));
	camera.pan = 90; camera.tilt = -90;
	
	theil_line3d(ent_node1.x, ent_node2.x, COLOR_RED, 100);
	theil_line3d(ent_node1.x, ent_node3.x, COLOR_RED, 100);
	
}


also alpha is only from 0...100, you have it set at 250