Co workers issues?

I have a random question that is actually weighing on my mind lately. I have never ever dealt with a similar situation before - and I would appreciate male thoughts on this mostly. I started a new job 4 months ago, and a month ago maybe more I realized that a coworker acts a bit differently around me, he is usually outgoing with everyone else but me. I believe this changed after he found out I was married - don't understand why though. I will catch him looking at me - he avoids me though, or is very quiet around me and would ignore me completely - but would still catch his eye once in a while. I am really very nice and outgoing and I actually genuinely like him - he is nice and smart, but for some reason I don't think he likes me - and in the upcoming months I will have to work with him so I want to kind of get on better terms with him.