I'm not quite sure what to do in this situation

Now I'm not the best player (silver 4 last season) and I have my share of bad games, but I also have good games. However sometimes when I play, my teammates die over and over again. I like to play toplane, but I don't roam very often. (my general plan is to take the outer turret before I start roaming) By the time the laning phase is over, I might be at an ok score of 2/1 or 2/0, but the other fed enemy might be like 6/0. I'll be somewhat strong, but when I die in 2 seconds that doesn't matter. I know that if I have a character with hard cc I could lock them down and kill them, but what if I play someone who can't do that? What do I do in this situation?

I think roaming earlier to help the losing lane out might stop the snowball, but I don't know if that is a good idea. Since they are dying a lot, I don't really trust their judgement or mechanical skill. Also if the roam doesn't work out I could end up giving them more kills or just lose out on farm and get behind in my lane.

Any tips?

tl;dr How do I deal with a fed opponent when I am in another lane and only am having an average game?