I belong to a gym for about half of the year, because from Christmas until summer generally I'm so busy with exams and coursework going to the gym either becomes a chore, or doesn't happen, or completely wears me out, so I generally just don't re-new until after exams.
But I love the gym. I'm a gym kind of person, I hate sport, I like running on one spot in a synthetic environment. That way I can just focus on exercising.Gosh I sound dull. I don't find it difficult to go, but I tend to go more often if me and my fiance are both members because if one of us is a bit like "maybe we should stay in bed?" (we tend to go first thing in the morning) the other goes "NO WE ARE GOING TO THE GYM"
So having a gym partner can be good, as long as you're not tempted to chat while you exercise or distract each other, or to get competitive. Unless you like that, but I've had competitive friends I've gone to the gym with and it's awful, they always had an eye on what settings/etc I was on and I just felt self conscious.
Gyms aren't for everybody, if you do join my advice would be to vary what you do, and use equipment to its full potential. For example, don't just stick the machine on the same setting every time, or you get used to it and you don't work as hard. I tend to do a combination of weights and cardio, and then a good 15 miniutes of stretching at the end. I can't believe how few people stretch, it's the best bit, it feels like "ahhhhhhhhhhhhhhhhhhhhhhh yeah".