You've only been on TRT for 2 months, you MAY NOT need Arimidex... You should only start taking it if after 3 to 6 months your estradiol levels are too hign (over 40 probably). I am a member of a TRT forum on Yahoo and many guys there have taken the stuff for 7 to 10 years so far... but TRT is only about 15 years old for men, so long term data is rare or non existant.
Most of the guys guage their E2 levels based on night and morning wood. E2 has to be well balanced in order for you to get any. Too high OR too low and you got a floppy at best.
Many of the guys just take DIM when they need to lower their levels. If levels get too low, then they have to basically stop the DIM and wait.
You might consider looking into the group...Hypogonadism2 in the yahoo groups.
(PS I've been on androgel for 14 months now and don't take an e2 inhibitor. My last tests put e2 at 38.6 so I started taking DIM twice a day.)