Eh, I think the forum is divided on this... personally, I can't think of anything more miserable than spending time on a treadmill.
If you're lifting real heavy, the kind where you are actually close to being out of breath after you put the weight down, you may not need any extras.
I've been told some of the traditional old 'cardio' is good as a follow-up to some HIIT activities, like if you hit the hill for some sprints some people say doing a short-ish jog after that helps as the initial HIIT session releases fatty acids that you can then 'burn' with your slow job. I have no idea if any of that is true.
You say you enjoy it though, so research it some, but better yet: experiment. Take some measurements and spend a month doing something one way, then see how it went for you and try something else. I think we want to be pick the perfect combination of things, but don't spend enough time finding out what things our actual bodies respond best to.
For instance. I'd like to sprint weekly right, but I don't do it, mostly because I have this stupid idea that if I don't sprint first thing in the morning then sprinting any other time is a waste of time. This is pretty wrong, sprinting at any hour is better than not doing it ever, but I was letting perfect be the enemy of good which ironically resulted in no activity at all. Another way to say this is, somebody who sprints in the afternoon is doing better than someone who never sprints, but the person sprinting first thing in the am is maybe doing a little better than the one that sprints in the afternoon... I hope that helps and isn't confusing.