Studying in Germany, TRV rejected. Help!

[stevenzhao]

Hello, everyone.
I am a Chinese girl studying in Germany right now. I have been to Germany for 5 years.
My boyfriend is studying in Canada with only a study permit. I want to apply visitor visa to see him.
Actually, I have applied TOURIST VISA successfully twice without telling I have a boyfriend during the Christmas Holiday last two year.
This year, I submit the application, still as a tourist, again right away after I came back from Canada.
I got rejected for two reasons as:
1.Your family ties in Canada and in your country of residence
2.Purpose of visit
3. proof of establishment or ties to country of residence
4.proof of status in country of residence

I want to apply again.
But this time I don't know which VISA I would better apply.
Visiting friend or Tourist?

I mean my boyfriend can send a invitation letter as a normal friend.(This I feel could make VO think I don't have immigration trend)
Is this way be more helpful
Or do I need still apply for tourist visa without telling any boyfriend information.

Thanks!everybody!