TL:DR: I don't think you can.
Potential issues to overcome:
- no history of income
Every country that is asked to admit a foreign national as a tourist, needs to ensure that person won't become a drain on resources provided for its citizens. You state your boyfriend is to provide your means to subsist. However, from Sweden's point of view, what if you break up? Then you would be on your own, with no means to live or (more importantly) return to your country of residence. Your personal income sounds like it isn't enough to live on, but rather it is just supplemental income. So what if, for whatever reason, you are forced to survive in Sweden without the assistance of your boyfriend? - reason to leave
Each country also wants to control its internal immigration numbers. They will allow only so many people to legally immigrate. More developed countries tend to have more people (esp from the undeveloped parts of the world) wanting to immigrate to them than they want to accept. People will come to them on visitor visas, and then never leave, becoming illegal immigrants. So Swedish officials need to know you have valid reasons to want to voluntarily leave. These are usually provided as strong family ties and/or work/school. You may have family residing in Kenya, but why are you going to Sweden? Not really to visit Sweden, but to visit your boyfriend (your 'family' as it were.) You are basically telling Sweden that you specifically won't want to leave. Your schooling doesn't really help, because as you say yourself, "I will be done with my studies this month."
Also, you gave your apartment lease. Is it a long term (yearly) or short (monthly)? If short, that provides no reason for you to return to it.
When it comes right down to it, I don't think you can improve your chances of getting a visitor visa, given your circumstances as you present them.
