visitor visa denied

hi if any can give me advise i applied for a visa and was recently denied the reasons 1) travel history) the travel history i showed was working visa going to iraq for work since 2008. (2) purpose of visit ( i got a letter of invite from a friend in canada) i just stated i wanted to visit during my time off from work which was from dec 23 until feb 17. i didn't mention that my friend has a partner (same sex) or that i really was interested to visit the school she works in and see the programs they have for special needs children and finally (3) weak ties to country. i included letter from my employer. bank statements tenants agreement, land title receipts that i pay my younger brothers college tuitions and provide for my mom and sister. share holder for a business i own with my brother.

they told me i can reapply if i can prove to change some of the conditions
can i show a travel history of countries i went that didn't require a visa for me as i am from uganda
when reapplying do i need another letter of invite to state the reason why i want to visit is to see the education they have in canda and some of the ideas i can take home i too am a teacher by profession and should she include her partners name on the letter.
any ideas are always welcomed for succeed.