Ok, first of all, yes, IMO it is possible to feel a spark towards a "nice" guy. I'm with one right now. He's very different from all my previous partners in that he's not a bad boy. He's a family oriented, driven, financially responsible, sensitive, communicative and easy-going guy. Not one bit like the thunderstorms I'm used to dating...And yet, there was a definite spark between us...there had been for over a decade but I was too busy trying to find my "bad boy" to give him a chance.
As for your situation, I wouldn't say that your man is "Mr. Nice Guy". He seems like he's Mr. Deceptive, in that he lied to you, and now he's trying to make up for things. That does not speak of having strong moral fiber (to me anyway).
Listen to your gut. You've already posted that you don't feel ready for anything. Go with that. I did go through a period of wanting nothing from no one. I threw myself into my hobby (tango) and went out on 1 date with a random guy, and it went absolutely nowhere. I was thrilled. A date without strings. Wonderful. I had lots of coffee dates with girlfriends, a couple of manicures, shopping trips with mom, cool and new activities with my baby girl, read a bunch of novels and slept a lot. Plan stuff like that out for yourself and enjoy!
Mr. Pretending To Be A Nice Guy can go find himself someone else to fool.