I've written my story before, about how I got started in the martial arts. At that time, I'd just started to train in Tae Kwon Do and Hap Ki Do.
Doing more than one discipline is difficult. While you'd think that the general principles of one would reinforce the other, there's also things that get in the way - prior learning that you have to unlearn and re-learn anew. It becomes a struggle to keep it all straight, to differentiate between styles.
You can't just rely on habit, you have to build new habits, one for each style.
I've kept at it. It's taken almost three years, but this week I tested for my Black Belt in Tae Kwon Do. I now hold two black belts - the other being second degree in Tang Soo Do. Not bad for a 53 year old guy who started training six and a half years ago.
Naturally, I'm not stopping. I'm going to continue to train so long as my body and my financial situation allows. There's still a black belt in Hap Ki Do to pursue, as well as higher degrees in these disciplines.
Find something you love doing, and keep doing it.