Jordi
I'm training for a marathon right now, and it takes up a lot of time. The long runs get a bit boring after 15 km, but I still have to push through. I never feel like doing them, but once I'm done, I'm always glad I did. What works for me is doing my longest run early in the week, right after work in the evening. This helps a lot — otherwise I'd spend the whole week dreading it.