Whats he deal with nigerian men? Why so many bad rumors?

I meet a guy this summer that's half nigerian and Jamaican. We meet online and chatted off and on about 2 months before we meet. Well since then we have been seeing each other consistently for about 3 months and I have been hearing alot of bad things since we have been getting closer. Since we really started seeing each other he would tell me all things he wants to do with and for me and how he needs to get his life together befcom mittsommitts to me. He has been pretty consistant with coming around and how he treats me. He asked me for something once because he was in a bad sitution and I said no and that was back about a month ago and nothing changed with us. If anything hes always talking about what he can do to make more money to take care of me. Last night he told me he wanted to finally be together and that hes falling for me. All this came about after I had my ex over one night and he got a little jealous and wouldnt talk to me for days. I really care about him and he seems to care about me too but Im scared to let my guard down because I heard about nigerian men scamming women and taking their money. Has anyone heard of any good experiences? Why are they labeled as bad?