He wants to marry me but why am i so unsure? he can be so mysterious! advice?

I am 26 and have been dating my partner who is 9 years older then me for 5 years and we live together, he was born in Puerto Rico but moved to Pennsylvania when he was 10 & is of Latin/Italian decent. When i met him i was completely drawn to him as he is very mysterious and he has a very raw, rugged kind of ual appeal. I love him like crazy and he almost always wants to be around me he is so intense and he goes out of his way to never get me mad or upset and constantly tells me he loves me. He really is one of the most mysterious people i've ever met he also exudes a dark, mysterious, confident personality and he has way to much energy, i know it sounds stupid but it feels like he never sleeps if i wake up to go to the bathroom and i look at him he's always looking at me once or twice i got creeped out but never thought twice about it. When im in bed with him im always in his arms and if im on my side of the bed he pulls me into him and arms all around me if i move again he'll pull me back to him, we have a fantastic life but it feels like its everyday. All my girlfriends love him and this he is so y and they almost always say he so intense is swarthy and probably capable of many dangerously lewd acts and he idolizes me. He asked me to marry him last weekend but i told him i needed time to think as all this stuff about him is stuck in my head and driving me crazy. He basically hates when we have to go out to parties or get togethers and tells me he would rather just have me alone or be at home with me and never really lets go of my hand. I do love him to bits but am i just having second thoughts? i really need advice?