How to win against a winning team as a top laner who's up against Nasus?

Ok so.. Good evening

I was just wondering if anyone has any idea what to do when you're the top laner against Nasus (me as Singed main) while everyone on your team is giving kills to the enemies and losing their turrets.

So I'll explain the situation, I get a level 2 kill on Nasus, freeze the lane and deny him farm for 15minutes. I had more then double his farm and he couldn't do anything anymore at that time. Meanwhile I notice enemy adc and mid lane are both quite fed and we start to lose those turrets. Maybe I should have roamed earlier but if I did that I gave Nasus freefarm because it's not like he backed a lot he just stood there for exp not even trying to get stacks anymore, so as soon as I left he'd start stacking and pushing as usual. Anyway, as soon as our mid and bot turret get taken and my team keeps on dying I decide to take top turret and roam. It was possibly already too late with a 8/1 annie and 6/1 enemy Jhin but well I could give it a try. As soon as I start roaming my teammates keep on mispositioning and I cant really give them kills if they die that way, nor 1v3 or anything so it's not like I can snowball real fast to get my teammates back in the game and so I can go stop Nasus again before I can't do it alone anymore. Five minutes pass after I start roaming, I've been busy defending other lanes as my teammates died often and when we finally managed to group and I finally engage a good teamfight that we win and get a turret from, Nasus takes my turret, and is only 70 cs behind anymore and I haven't been able to really make my team catch up yet. I go back top for a little while to push the lane and my teammates start dying again and we lose another infernal drake. Nasus tp's back top and I notice he's completely counterbuilding me so it's not like he can kill me but it goes both ways, I cant kill him neither on my own, nor zone him anymore. Literally at that point I realized it was completely over, if teammates would come top to really stop nasus, enemies do the same and win top or they just group elsewhere as they are fed and we cant stop them without a numbers advantage neither.

So did I have to roam earlier and hope that Nasus isn't as good at stacking and pushing as I could be snowballing my team and trying to end it fast or maybe tell my botlane to lane switch so they could maybe get fed off nasus and freefarm there earlier? Or was it just one of those games that's not winnable?

The reason I'm asking this is because I know exactly how to play against Nasus as Singed, As long as my team isn't losing that hard resulting in constantly losing objectives(/they are still able to defend a little atleast), I always win as I don't have to babysit them and can just roam a few small times to get them back in the game if needed, but every time that my team is losing objectives everywhere and I try to help them make a comeback and get objectives (but it's more of a babysit job half the time) I lose the matchup. It might just be a game that cant really be won as it's a team game and if the enemy has 4 better players they naturally win, but maybe someone has any sort of pro advice I could use or try in the future.

Thanks if you read this far Friendly regards, Headnods