Every football fan of measurable loyalty knows they're bound to a contract. At any given moment your weekend may be ruined – abruptly, all at once, and probably by someone who until then didn't seem much capable of influencing your life, like Steve Sidwell. I'm a Spurs fan, so chalk up the blighting of otherwise happy times to Winston Reid, and Glenn Whelan, and that lino who missed the goal at Old Trafford that time. I had no great need for an enhanced way for this sport to upset me: and yet, about five years ago, I signed up for a fantasy football league. It has become clear this was a mistake.

Patjim Kasami scored a chest-and-volley for Fulham last month that was thrilling, unforgettable, as good as that bit in Apollo 13 where they don't burn up on re-entry – and I watched it miserably. Kasami was in my fantasy football team but I'd left him on the bench.

No points for a player on the bench and no points, obviously, for a player who's not in your team at all. While the friends I play fantasy football against had identified Romelu Lukaku as a reliable point-grabber, I clung stubbornly to my start-of-season selection, Roberto Soldado. And Soldado, towards the end of October, did score a few; but by then I'd ditched him to bring in the free-scoring Lukaku. Who immediately stopped scoring. Fantasy football, with its transfer budgets and formation dilemmas, is meant to make you feel like a manager. What it actually makes you feel like is a bungling, low-rung god, accidentally malevolent and only able to curse those you want to foster.

Listening to the radio on a Saturday afternoon, it used to be that updates had to be coming in from White Hart Lane, or wherever Spurs were playing, for me to tense up. But as a fantasy manager the bad news comes in from everywhere. Southampton have conceded! (So their goalkeeper won't earn me points for a clean sheet.) Everton have subbed Ross Barkley! (I knew I should've given the spot to Steven Naismith.)

Tony Blair, misunderstanding superbly, once talked up fantasy football as a good way to practise maths. This was in 2000 and the game was still played in print, managers asked to frown over lists in the newspaper, adding up the achievements of Muzzy Izzet and Alen Boksic. Since the game migrated online, that little bit of arithmetic has gone; software automatically digests the weekend's goals and assists, totalling your points and delivering a verdict that can be devastating. I still wince at the 17 points missed when Luis Suárez scored an October hat-trick.

By the way, Blair was right to judge there are life lessons to be learned from fantasy football. One: Fernando Torres isn't worth the money. Two: beware of tinkering. (I have, shamefully, completed entire seasons of intricate transfer dealing, noticing afterwards that I'd have won more points if I'd left my XI alone from the start.) Three: there's nothing so motivating as the fear of letting down a friend. Leighton Baines, having scored twice in one game for Everton in September, said afterwards he was spurred on by team‑mate Leon Osman, who'd "taken me out of his fantasy football team because I wasn't doing enough". Baines vowed to score a couple, and did.

I'm not sure which version of the game Osman prefers, but I like the one on Fantasy.PremierLeague.com. (Also favoured by Peter Crouch. And Crouch plays properly: last season he dropped himself because he just wasn't performing.) I'm loyal to "Fantasy Prem" because it's free; because you can design your own kit, for instance the teal-and-lemon combo I'm trying to popularise; and because after five seasons as an also-ran in my mini-league, I want to hang around and win the thing. Problematically, I play against a group of psychic Mourinhos who can take in a couple of Match of the Days and deduce that Loïc Rémy is on the verge of a scoring bonanza. How do they know?

Not everyone competes on a level plane. Andy Murray is a devoted fantasy football man. Last season, between winning the US Open and Wimbledon, the Scot topped a mini-league among friends and even awarded himself a little trophy. But he admitted he'd had outside help. Wondering whether to keep or drop the injured Michael Dawson, Murray had simply sent Dawson a text. "He said I should drop him."

Prince Abdullah of Saudi Arabia once telephoned George Gillett, then co-owner of Liverpool, to find out whether Steven Gerrard was due to start at the weekend, not wanting to waste the spot in his lineup otherwise. Explaining his passion for fantasy football, Prince Abdullah said: "When you've got a player from Norwich City in your team [it means that] every game matters." This was my thinking when I signed up. How exciting, I thought, to have something to root for while watching Norwich. I was foolish.

Like many Tottenham supporters, I believe myself unfairly prone to sorrow. And it used to be lovely to slump in front of a game from Carrow Road, nothing at stake. Now? Now I'll sit there chuntering at a well-meaning mediocrity like Steven Whittaker, hoping he'll bundle the ball in off a long throw, or play for a point-earning 60 minutes without getting a yellow. It's exhausting.

Last season, preparing for a match with Manchester United, West Brom goalie Ben Foster dropped Robin van Persie from his fantasy squad. Foster's reasoning, I guess, was that when a Van Persie shot came rifling at him during the match, he didn't want to be in two minds. Save it, or take the points? Fantasy football can be deranging like that.

The novelist Sebastian Faulks has noted its strange effects, having once watched his son fine-tune a fantasy team on his laptop while a live match played out on TV. Faulks observed: "The fantasy football game, which depended on the real result, was actually more important to my son than the real game. I became aware [of] our willingness to live our lives at one remove from reality." Faulks put the idea into a novel, A Week in December, creating a character called Finn who was a fantasy football obsessive. Poor Finn. He ended up in a psychiatric unit, wrecked, sedated, "unseeing".

Before this happens to me, I plan to give up. Not yet, though. I've climbed to sixth in my mini-league and I'm finally ready to make a concerted push on the top four.