I'm in bronze. A large percentage of times I play ADC, my support think his or her job is done once we lose a turret. Even if it's really early in the game, they seem to think the protocol is "we lost a turret, lane lost, time to go mid." This has happened to me a lot.
Why does this happen?
HentRex3 votesI'm only Silver, but most of the time the enemy bot lane will rotate mid. So that ends up making it a 3v1 there. Plus now bot is a long lane and so is "unsafe" for the enemy to continue pushing to inner tower. Now if they stay bot so should the support.
360D3GR3SS1 votesWell In higherish elo I usually leave my adc once I see they have a lead and don't throw it away blindly. If I don't think they are competent enough I just stay with them unless asked to leave.
3tyson1 voteswhen you pick 
HaIlMonitor1 votesI always leave if my ADC blows.... I am a jungler main though so i just turn into a gank/ward bot!
Player of Games1 votesWell for low elo like that you almost certainly cannot rely on your ADC to have the raw skill to be safe whilst solo. Even with adequate ward coverage, people are overly greedy and then will blame you when you leave them. There are a multitude of situations however in which you should take advantage of a roam;
If you took the enemy bot lanes tower and your tower isn't in danger of being counter-sieged
The enemy bot lane is freezing the wave near their tower in an attempt to catch up in gold/xp, in this case you want to roam mid immediately and pressure the tower for the 3v1. This will force their jungler and/or support to counter-roam or else they risk losing the most important tower on the map.
You're aware that the enemy support is roaming mid or top, in this case you want to force down bot tower asap and attempt a dive if safe, or counter-roam to another lane and tell your adc to be safe.
Finally, you should try and roam mid immediately after you get Mobi boots as early as possible. A lot of people still don't expect the support to roam mid very early and you can catch people off guard if done right, just let your adc know you're leaving.
You can also opt to roam with your jungler for a 3 man gank, these are typically very unexpected and can go very well if executed properly.
Baunjo1 votesThe support can leave lane whenever they want, but honestly I feel like whenever i see a better opportunity to do something productive I will leave
