Sooooo.. this has absolutely nothing to do with Ana but I need help..

Right lovely ladies... I need some advice.

A male friend of mine(we'll call him S) recently confessed that he likes me, but me and his best friend(we'll call him D) only broke up a few days ago (for the 2nd time in 1 month). He wanted to wait before he told me but he'd been harbouring the secret for a few months and wanted to get it off his chest for a while. 

The thing is, S was there for me more than D over the past few months. S supported me when I'd had a bad day and D was too self absorbed to care and just told me to get over it, or talked about how shit his day had been, meaning he hadn't done anything and had been bored all day. S even took my side when D cheated on me then broke up with me, just after our anniversary, by text and with phrasing that made me feel like it was my fault. (he didn't confess to the affair until a week after, when I'd calmed down over the matter, which made it all come back again.) S helped me regain my confidence to face the world again. I don't depend on him, please don't get that idea, but he's sweet to me and always makes me smile, he's a true gentleman. We get along really well, and we always have something to talk about, whereas with D it would always be music filled quiet, or talk about him and his 'horrible' life. 

I am beginning to feel like I have feelings for S, but I don't want it to be a whole rebound situation. I'm definitely over D, we got back together and I called it off because it just didn't feel right, I didn't have any emotional attraction or trust with D anymore, yet even at that time I felt I could trust S with my life, and there may have been an attraction there that I didn't notice.. 

I don't want S to think I only like him because he likes me, or that I'm rebounding onto him. S has said he would like to be friends as we are now and his feelings not interfere with that, so I was thinking maybe give it a few weeks and see if I still feel the same? Or should I jump on the opportunity while I still have it?

I just don't really know what to do, this hasn't actually happened before..