Hi Mustang,
Welcome to the pain board. First of all, liking a med because it is working well for you is not abusing it, I have been on tramadol for 12 years, and take 6-8 pills a day, and have not had any bad side effects from it. If your prescription says to take 1-2 pills every 4 hours as needed, you arent abusing your meds.
The reason it also works for depression is that it has something in it similar to prozac, If you do need to go off the ultram (tramadol) it might help to simply have your doctor raise your dose on your prozac.
If you do feel strongly that this is in fact an addiction, it is important to let your doctor know, believe me, they would rather hear it from you than find out another way, and he can help you make decisions on how you want to proceed. There is also an addiction board on this site, that may help you as well.
Good luck and please let us know how you are doing, whatever you decide.
Your Friend, Fabby