Hmm... how to answer this one - you sure you're not gay? *lol*
nah, I get the same from time to time. I love sex and so does my girlfriend, but I am expected to make the moves if I want it, so often I don't bother - probably from laziness or whatever... I wouldn't say it's like a chore or anything, sometimes I just lack the effort. That's not to say we don't have lots of sex, but definitely not as much as we used to.
Another thing is maybe you're not as attracted sexually to your girlfriend as you once were (i.e. bored). If you've been with her for quite a while, you might not feel driven to have sex as much, since you've "done it all before". My girlfriend is very attractive - you would think I want to have sex whenever possible - but I suppose I don't nowadays. We have done it in every room, every position, every everything (within reason!) and now I suppose it hasn't the same appeal.
My advice to you is you should probably try to have it as often as possible - or at least more! Most of the time, if the sex and affection is not satisfactory, the relationship will eventually suffer. Every relationship is different, but that can be said as a general statement for most of them. You need to get back some spark, some spontaneity, maybe some toys and lingerie....
It depends also on her, of course. If she is not the type to really enjoy sex (be it shyness, low confidence, self awareness etc.) and doesn't mind at all not having sex for months at a time, then at least try and have a big night once in a while. That way you can both enjoy it when you do, and don't expect it any other time.
Of course, it could also be a product of your finasteride regime. Having suffered no symptoms sexually from it, I cannot really comment.... except, I hope for your sake it's just laziness! :wink: