most f2p games are complete and utter garbage ngl. you say you can pirate single player games, stick with that for the most part. Recently I've been getting into visual novels (if you can even call those video games) which are decent copes. also american or euro truck simulator 2 for comfy gaming (american has better views, euro has more content, so basically quality or quantity). anyway, here's my f2p suggestions.
-league of legends specifically for aram, probably my favorite vidya cope atm
-runescape is fun for a while until it starts taking hours to level up skills once. pvm and pvp stress me out to much to even try them.
-team fortress 2 for a decent fps. im bored of it now, but only because I put in 500 hours before getting to that point.
-also csgo recently went f2p, you could try that as well.
-path of exile if you want a great time sink and have a lot of patience. I play it on and off, usually uninstalling in a fit of rage because I kept dying on a poorly geared character.
-clicker games can certainly be good time killers, but they're mostly suited to being a side or background kind of game. My personal favorite is realm grinder.
-guild wars 2 sucks donkey dick imo. tried it after angryjoe (soy) praised it, and I found there was absolutely nothing special or different from other mmo's. If you want to play a quality mmo, the only real options are osrs and wow (maybe ffiv if you like the lore). ignore everything else ded srs.
-hearthstone is the best ccg if you're into that weird shit.