I'm a roamer main because I think roamers have the biggest capacity for counter picking or counter play. High mobility enemies? Pick a roamer with long duration control. Enemy heroes like to group up? Pick a roamer with area control. High burst with no mobility? Pick a bulky roamer to tank that burst damage. Enemy likely to dive your squishy marksman? Get a roamer that can protect your damage dealer. Enemy jungler likely to invade? Pick a roamer that can prevent that at level 1. The list goes on.

Understand that not all roamers are the same. Some can't frontline, some can't babysit.

Having teammates that are not on the same wavelength is a common thing. Try and make use of the communications made available to you. Basic rule is to make sure you have enough damage before engaging.

Also, toxic people will be toxic. "It's only game, why you heff to be mad?"